We don't require birthdate. If you prefer not to include it we certainly understand.
We use birthdates in Stretch to remind your family but especially your Tribe (typically extended family) when your birthday is (so you can get lots of presents -- OK, we don't know about that part).
Stretch follows the COPPA regulations for the online privacy of users under 13. We like to know whether consent is required by parents or guardians and take special care with supporting children under 13.