There are four age divisions: 12, 14, 16 & 18 and under. You may play in your age division up until the last day of the month before you “age out”. For example, if you are 12 years old & are going to turn 13 in May, you may play in the 12-and-under division until the last day in April.
For 10 and Under players
https://netgeneration.usta.com/us-en/the-net-generation-playtracker.html