We require date of birth information to verify age. VOMO requires all users to comply with the U.S. Child Online Privacy Protection Act, and does not allow anyone under the age of 13 to create their own account. (see section G, item 3, "Can I block children under 13 from my general audience website or online service?" in the link above)
There are also projects on the platform that are open only to volunteers above the age of 13 and 18. In our efforts to provide a safe platform for children and families while also allowing for volunteer projects that only adults can sign up for, we require a birthdate for every single user in the platform with a minimum age of 13 years old on the day of signing up.