You automatically get a new license with the under 21 notation removed. Remember, it is important to always keep your address updated on all DMV records (p.s. - registration and license records are separate)
Yes, you need to get a new one when you turn 21. I believe they send info in the mail as you are about to turn. When you renew it, they will give you a temporary license that is really just a piece of paper. This acts as your license in the time between your old license expiring and you getting your 'over 21' license in the mail.
Hope this helps. https://nysdmv.custhelp.com/app/answers/detail/a_id/172/~/how-to-remove-the-words-“under-21”-from-your-driver-license
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