:/

```
1.9.3p374 :001 > User.joins(person: :profile).where("profiles.birthday > date_sub(now(), interval 13 year)")
  User Load (0.7ms)  SELECT "users".* FROM "users" INNER JOIN "people" ON "people"."owner_id" = "users"."id" INNER JOIN "profiles" ON "profiles"."person_id" = "people"."id" WHERE (profiles.birthday > date_sub(now(), interval 13 year))
ActiveRecord::StatementInvalid: PG::Error: ERROR:  syntax error at or near "13"
LINE 1: ...HERE (profiles.birthday > date_sub(now(), interval 13 year))
```