There is an ATT app, which should be on his phone already.
"Usage manager". It looks like a bar chart. It may be buried in a folder of ATT stuff on his phone.
It has 3 tabs for battery use, apps and data. From the data tab, you can tap menu and restrict background data, and cap his data use. (No password required, but he can change the cap.)
you will have to set some consequence for exceeding data use. He doesn't need YouTube over cellular. Next stop is turning off his data at the account level once ge hits the limit. Boys are more "cause and effect" learners. LOL. Been there! (Still there)
