feat: replace age integer with date_of_birth across backend and client

Store date_of_birth (DATE) instead of a static age integer so that age
is always computed dynamically from the stored date of birth.

- Migration 011: adds date_of_birth, backfills from age, drops age
- AgeFromDOB helper computes current age from YYYY-MM-DD string
- User model, repository SQL, and service validation updated
- Flutter: User.age becomes a computed getter; profile edit screen
  uses a date picker bounded to [today-120y, today-10y]

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/user/calories.go

@@ -1,6 +1,9 @@
 package user
 
-import "math"
+import (
+	"math"
+	"time"
+)
 
 // Activity level multipliers (Mifflin-St Jeor).
 var activityMultiplier = map[string]float64{
@@ -16,6 +19,23 @@ var goalAdjustment = map[string]float64{
 	"gain":     300,
 }
 
+// AgeFromDOB computes age in years from a "YYYY-MM-DD" string. Returns nil on error.
+func AgeFromDOB(dob *string) *int {
+	if dob == nil {
+		return nil
+	}
+	t, err := time.Parse("2006-01-02", *dob)
+	if err != nil {
+		return nil
+	}
+	now := time.Now()
+	years := now.Year() - t.Year()
+	if now.Month() < t.Month() || (now.Month() == t.Month() && now.Day() < t.Day()) {
+		years--
+	}
+	return &years
+}
+
 // CalculateDailyCalories computes the daily calorie target using the
 // Mifflin-St Jeor equation. Returns nil if any required parameter is missing.
 func CalculateDailyCalories(heightCM *int, weightKG *float64, age *int, gender, activity, goal *string) *int {

backend/internal/user/calories_test.go

@@ -2,10 +2,48 @@ package user
 
 import (
 	"testing"
+	"time"
 )
 
 func ptr[T any](v T) *T { return &v }
 
+func TestAgeFromDOB_Nil(t *testing.T) {
+	if AgeFromDOB(nil) != nil {
+		t.Fatal("expected nil for nil input")
+	}
+}
+
+func TestAgeFromDOB_InvalidFormat(t *testing.T) {
+	s := "not-a-date"
+	if AgeFromDOB(&s) != nil {
+		t.Fatal("expected nil for invalid format")
+	}
+}
+
+func TestAgeFromDOB_ExactAge(t *testing.T) {
+	dob := time.Now().AddDate(-30, 0, 0).Format("2006-01-02")
+	age := AgeFromDOB(&dob)
+	if age == nil {
+		t.Fatal("expected non-nil result")
+	}
+	if *age != 30 {
+		t.Errorf("expected 30, got %d", *age)
+	}
+}
+
+func TestAgeFromDOB_BeforeBirthday(t *testing.T) {
+	// Birthday is one day in the future relative to today-25y, so age should be 24
+	now := time.Now()
+	dob := time.Date(now.Year()-25, now.Month(), now.Day()+1, 0, 0, 0, 0, time.UTC).Format("2006-01-02")
+	age := AgeFromDOB(&dob)
+	if age == nil {
+		t.Fatal("expected non-nil result")
+	}
+	if *age != 24 {
+		t.Errorf("expected 24, got %d", *age)
+	}
+}
+
 func TestCalculateDailyCalories_MaleMaintain(t *testing.T) {
 	cal := CalculateDailyCalories(ptr(180), ptr(80.0), ptr(30), ptr("male"), ptr("moderate"), ptr("maintain"))
 	if cal == nil {

backend/internal/user/model.go

@@ -13,7 +13,7 @@ type User struct {
 	AvatarURL     *string         `json:"avatar_url"`
 	HeightCM      *int            `json:"height_cm"`
 	WeightKG      *float64        `json:"weight_kg"`
-	Age           *int            `json:"age"`
+	DateOfBirth   *string         `json:"date_of_birth"`
 	Gender        *string         `json:"gender"`
 	Activity      *string         `json:"activity"`
 	Goal          *string         `json:"goal"`
@@ -28,7 +28,7 @@ type UpdateProfileRequest struct {
 	Name          *string          `json:"name"`
 	HeightCM      *int             `json:"height_cm"`
 	WeightKG      *float64         `json:"weight_kg"`
-	Age           *int             `json:"age"`
+	DateOfBirth   *string          `json:"date_of_birth"`
 	Gender        *string          `json:"gender"`
 	Activity      *string          `json:"activity"`
 	Goal          *string          `json:"goal"`
@@ -39,6 +39,6 @@ type UpdateProfileRequest struct {
 // HasBodyParams returns true if any body parameter is being updated
 // that would require recalculation of daily calories.
 func (r *UpdateProfileRequest) HasBodyParams() bool {
-	return r.HeightCM != nil || r.WeightKG != nil || r.Age != nil ||
+	return r.HeightCM != nil || r.WeightKG != nil || r.DateOfBirth != nil ||
 		r.Gender != nil || r.Activity != nil || r.Goal != nil
 }

backend/internal/user/repository.go

@@ -45,7 +45,7 @@ func (r *Repository) UpsertByFirebaseUID(ctx context.Context, uid, email, name,
 			avatar_url = COALESCE(EXCLUDED.avatar_url, users.avatar_url),
 			updated_at = now()
 		RETURNING id, firebase_uid, email, name, avatar_url,
-			height_cm, weight_kg, age, gender, activity, goal, daily_calories,
+			height_cm, weight_kg, date_of_birth, gender, activity, goal, daily_calories,
 			plan, preferences, created_at, updated_at`
 
 	return r.scanUser(r.pool.QueryRow(ctx, query, uid, email, name, avatarPtr))
@@ -54,7 +54,7 @@ func (r *Repository) UpsertByFirebaseUID(ctx context.Context, uid, email, name,
 func (r *Repository) GetByID(ctx context.Context, id string) (*User, error) {
 	query := `
 		SELECT id, firebase_uid, email, name, avatar_url,
-			height_cm, weight_kg, age, gender, activity, goal, daily_calories,
+			height_cm, weight_kg, date_of_birth, gender, activity, goal, daily_calories,
 			plan, preferences, created_at, updated_at
 		FROM users WHERE id = $1`
 
@@ -91,9 +91,9 @@ func buildUpdateQuery(id string, req UpdateProfileRequest) (string, []interface{
 		args = append(args, *req.WeightKG)
 		argIdx++
 	}
-	if req.Age != nil {
-		setClauses = append(setClauses, fmt.Sprintf("age = $%d", argIdx))
-		args = append(args, *req.Age)
+	if req.DateOfBirth != nil {
+		setClauses = append(setClauses, fmt.Sprintf("date_of_birth = $%d", argIdx))
+		args = append(args, *req.DateOfBirth)
 		argIdx++
 	}
 	if req.Gender != nil {
@@ -132,7 +132,7 @@ func buildUpdateQuery(id string, req UpdateProfileRequest) (string, []interface{
 		UPDATE users SET %s
 		WHERE id = $%d
 		RETURNING id, firebase_uid, email, name, avatar_url,
-			height_cm, weight_kg, age, gender, activity, goal, daily_calories,
+			height_cm, weight_kg, date_of_birth, gender, activity, goal, daily_calories,
 			plan, preferences, created_at, updated_at`,
 		strings.Join(setClauses, ", "), argIdx)
 	args = append(args, id)
@@ -184,7 +184,7 @@ func (r *Repository) SetRefreshToken(ctx context.Context, id, token string, expi
 func (r *Repository) FindByRefreshToken(ctx context.Context, token string) (*User, error) {
 	query := `
 		SELECT id, firebase_uid, email, name, avatar_url,
-			height_cm, weight_kg, age, gender, activity, goal, daily_calories,
+			height_cm, weight_kg, date_of_birth, gender, activity, goal, daily_calories,
 			plan, preferences, created_at, updated_at
 		FROM users
 		WHERE refresh_token = $1 AND token_expires_at > now()`
@@ -205,14 +205,19 @@ type scannable interface {
 func (r *Repository) scanUser(row scannable) (*User, error) {
 	var u User
 	var prefs []byte
+	var dob *time.Time
 	err := row.Scan(
 		&u.ID, &u.FirebaseUID, &u.Email, &u.Name, &u.AvatarURL,
-		&u.HeightCM, &u.WeightKG, &u.Age, &u.Gender, &u.Activity, &u.Goal, &u.DailyCalories,
+		&u.HeightCM, &u.WeightKG, &dob, &u.Gender, &u.Activity, &u.Goal, &u.DailyCalories,
 		&u.Plan, &prefs, &u.CreatedAt, &u.UpdatedAt,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("scan user: %w", err)
 	}
+	if dob != nil {
+		s := dob.Format("2006-01-02")
+		u.DateOfBirth = &s
+	}
 	u.Preferences = json.RawMessage(prefs)
 	return &u, nil
 }

backend/internal/user/repository_integration_test.go

@@ -100,17 +100,17 @@ func TestRepository_Update_MultipleFields(t *testing.T) {
 	created, _ := repo.UpsertByFirebaseUID(ctx, "fb-multi", "multi@example.com", "Multi User", "")
 	height := 175
 	weight := 70.5
-	age := 25
+	dob := "2001-03-09"
 	gender := "male"
 	activity := "moderate"
 	goal := "maintain"
 	u, err := repo.Update(ctx, created.ID, UpdateProfileRequest{
-		HeightCM: &height,
-		WeightKG: &weight,
-		Age:      &age,
-		Gender:   &gender,
-		Activity: &activity,
-		Goal:     &goal,
+		HeightCM:    &height,
+		WeightKG:    &weight,
+		DateOfBirth: &dob,
+		Gender:      &gender,
+		Activity:    &activity,
+		Goal:        &goal,
 	})
 	if err != nil {
 		t.Fatalf("unexpected error: %v", err)

backend/internal/user/service.go

@@ -3,6 +3,7 @@ package user
 import (
 	"context"
 	"fmt"
+	"time"
 )
 
 type Service struct {
@@ -46,10 +47,11 @@ func (s *Service) UpdateProfile(ctx context.Context, userID string, req UpdatePr
 	if req.WeightKG != nil {
 		weight = req.WeightKG
 	}
-	age := current.Age
-	if req.Age != nil {
-		age = req.Age
+	dob := current.DateOfBirth
+	if req.DateOfBirth != nil {
+		dob = req.DateOfBirth
 	}
+	age := AgeFromDOB(dob)
 	gender := current.Gender
 	if req.Gender != nil {
 		gender = req.Gender
@@ -89,9 +91,17 @@ func validateProfileRequest(req UpdateProfileRequest) error {
 			return fmt.Errorf("weight_kg must be between 30 and 300")
 		}
 	}
-	if req.Age != nil {
-		if *req.Age < 10 || *req.Age > 120 {
-			return fmt.Errorf("age must be between 10 and 120")
+	if req.DateOfBirth != nil {
+		t, err := time.Parse("2006-01-02", *req.DateOfBirth)
+		if err != nil {
+			return fmt.Errorf("date_of_birth must be in YYYY-MM-DD format")
+		}
+		if t.After(time.Now()) {
+			return fmt.Errorf("date_of_birth cannot be in the future")
+		}
+		age := AgeFromDOB(req.DateOfBirth)
+		if *age < 10 || *age > 120 {
+			return fmt.Errorf("date_of_birth must yield an age between 10 and 120")
 		}
 	}
 	if req.Gender != nil {

backend/internal/user/service_test.go

@@ -94,19 +94,20 @@ func TestUpdateProfile_NameOnly(t *testing.T) {
 }
 
 func TestUpdateProfile_WithCaloriesRecalculation(t *testing.T) {
+	dob := time.Now().AddDate(-30, 0, 0).Format("2006-01-02")
 	profileReq := UpdateProfileRequest{
-		HeightCM: ptrInt(180),
-		WeightKG: ptrFloat(80),
-		Age:      ptrInt(30),
-		Gender:   ptrStr("male"),
-		Activity: ptrStr("moderate"),
-		Goal:     ptrStr("maintain"),
+		HeightCM:    ptrInt(180),
+		WeightKG:    ptrFloat(80),
+		DateOfBirth: &dob,
+		Gender:      ptrStr("male"),
+		Activity:    ptrStr("moderate"),
+		Goal:        ptrStr("maintain"),
 	}
 	finalUser := &User{
 		ID:            "user-1",
 		HeightCM:      ptrInt(180),
 		WeightKG:      ptrFloat(80),
-		Age:           ptrInt(30),
+		DateOfBirth:   &dob,
 		Gender:        ptrStr("male"),
 		Activity:      ptrStr("moderate"),
 		Goal:          ptrStr("maintain"),
@@ -178,19 +179,31 @@ func TestUpdateProfile_InvalidWeight_TooHigh(t *testing.T) {
 	}
 }
 
-func TestUpdateProfile_InvalidAge_TooLow(t *testing.T) {
+func TestUpdateProfile_InvalidDOB_TooRecent(t *testing.T) {
 	svc := NewService(&mockUserRepo{})
+	dob := time.Now().AddDate(-5, 0, 0).Format("2006-01-02")
 
-	_, err := svc.UpdateProfile(context.Background(), "user-1", UpdateProfileRequest{Age: ptrInt(5)})
+	_, err := svc.UpdateProfile(context.Background(), "user-1", UpdateProfileRequest{DateOfBirth: &dob})
 	if err == nil {
 		t.Fatal("expected validation error")
 	}
 }
 
-func TestUpdateProfile_InvalidAge_TooHigh(t *testing.T) {
+func TestUpdateProfile_InvalidDOB_TooOld(t *testing.T) {
 	svc := NewService(&mockUserRepo{})
+	dob := time.Now().AddDate(-150, 0, 0).Format("2006-01-02")
 
-	_, err := svc.UpdateProfile(context.Background(), "user-1", UpdateProfileRequest{Age: ptrInt(150)})
+	_, err := svc.UpdateProfile(context.Background(), "user-1", UpdateProfileRequest{DateOfBirth: &dob})
+	if err == nil {
+		t.Fatal("expected validation error")
+	}
+}
+
+func TestUpdateProfile_InvalidDOB_BadFormat(t *testing.T) {
+	svc := NewService(&mockUserRepo{})
+	dob := "not-a-date"
+
+	_, err := svc.UpdateProfile(context.Background(), "user-1", UpdateProfileRequest{DateOfBirth: &dob})
 	if err == nil {
 		t.Fatal("expected validation error")
 	}

backend/migrations/011_replace_age_with_date_of_birth.sql

@@ -0,0 +1,13 @@
+-- +goose Up
+ALTER TABLE users ADD COLUMN date_of_birth DATE;
+UPDATE users
+    SET date_of_birth = (CURRENT_DATE - (age * INTERVAL '1 year'))::DATE
+    WHERE age IS NOT NULL;
+ALTER TABLE users DROP COLUMN age;
+
+-- +goose Down
+ALTER TABLE users ADD COLUMN age SMALLINT;
+UPDATE users
+    SET age = EXTRACT(YEAR FROM AGE(CURRENT_DATE, date_of_birth))::SMALLINT
+    WHERE date_of_birth IS NOT NULL;
+ALTER TABLE users DROP COLUMN date_of_birth;