I was thinking 13 myself, I want the character to go through a lot of changes and do things he never would of done had he not left his self isolating environment. But I dunno, 13 might be a little too young. Maybe 15 or 16 so he could better pass as an adult.
The age would depend on what kind of situations you want the character to go through, but then again, you can have a 13 year old going through some shyt that would stress out a 19 year old, and that would only amplify the intensity and raise the stakes.
shyt just follow your artistic integrity breh