I think you are looking for m8 bosses as rears are usually m10 but do confirm. Treat yourself to some ti ones, they are much lighter than the stock ones, I do this on all my keeper frames and forks where I can. You can usually pick up a pair for under a tenner on eBay. Yes, you can't see them once fitted, but you know
Nothing wrong with that, my 10 year old was rocking Sid's and crossmax and carbon x9. Actually, might not be a great move, getting a taste for the exotic at an early could get expensive, though he may be getting a ti frame soon, if only he did more than ride to school