Extra SQL en Django. 2

models.py

from django.db import models
from django.utils improt timezone

class Person(models.Model):
    first_name = models.CharField(max_length=42)
    last_name = models.CharField(max_length=42)
    birth_date = models.DateField()

    @property
    def age(self):
        now = timezone.now()
        years = now.year - self.birth_date.year
        if now.month < self.birth_date.month:
            age -= 1
        elif now.month == self.birth_date.month and now.day < birth_date.day:
            age -= 1
        return age