I would say it's what you feel comfortable with.
The most important thing, whether or not you let him use it is to make sure he knows the proper way to work with all tools. Take the mystery out of it for him so he's not tempted to try to use it behind your back, which could definitely end badly.
I'm 24 years old and even just today I cut myself a bit with my rotary. Whoops!
Good luck!