Django Annotate Age from Birth Date

models.py

from django.db import models
from django.db.models import Count, ExpressionWrapper, F, Case, When
from django.utils import timezone


class PersonQuerySet(models.QuerySet):

    def with_age(self):
        now = timezone.now()
        age_expr = ExpressionWrapper(
            Case(
                When(birth_date__month__gte=now.month, birth_date__day__gt=now.day, then=now.year - F('birth_date__year') - 1),
                default=now.year - F('birth_date__year'),
            ),
            output_field=models.IntegerField()
        )
        return self.annotate(age=age_expr)


class Person(models.Model):
    ...
    birth_date = models.DateField()
    objects = PersonQuerySet.as_manager()