Well I am 20 but I turn 21 next month. Does that make a difference?
Since you are within 40 days of your 21st birthday, you won't have to do anything different. Your new ID won't have "Under 21" printed on it.
OK so my friend is 2 months away from turning 21. Will she have to do anything different?
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.