Photos will really help.
Also, I understand that gear isn't cheap, but kids will be kids. If I picked up on this sport at a young age, I know for sure I'd be super into jibbing and other park stuff. Hell, I'm trying to get into jibbing now lol.
If he truly enjoys riding over rocks and jibbing trees and stuff, then I say let him. Just tell him to be safe and enjoy
Base damage is just part of the game even if you aren't riding rocks and jibbing. I rode over some big rocks in Tahoe and it was really fun actually
Took my brand new Never Summer Proto into the trees and rode over a lot of branches and fallen trees. That was fun too haha.
One solution could be to pick up a beater board for your son. Like a cheap craigslist one? Let him beat that one up for when he wants to do that type of riding.