Make sure that you always change your birthday, even if it’s a wrong one, to 13 years of age or older to be able to change it at a later date. How to change your age on Roblox account (PC desktop)?

Roblox developers have until December 3 to update their games to comply with the new labelling system, or they'll be excluded from under-13 players by default.

Also, users under 13 years of age will not be able to directly message players outside of games unless they have parental permission.