If they renew it more than 41 days before their 21st birthday, it will still have "Under 21" on that so if they can wait, they should wait until less than 40 days until their birthday.
Thanks. Can I go online to renew my ID or do I have to go to the DMV to get it?
Either one is fine. You can renew online and your ID will be just as the same as if you went to the DMV.
I've been hearing about enhanced IDs but I don't know if mine is one of those. How do I know?