[masraum]

It's true, at 9yo, just any lock blade that's not too large and not too small for low cost is probably plenty of knife.

I like liner locks, but I would probably avoid them for a youngster. Benchmade makes an "Axis" lock which is very nice, but for someone young, a lock back which pretty much requires two hands to operate is probably better. The only thing that I would worry about with a lockback is that he would need to be strong enough to operate without having to try too hard. If he has too hard a time and is straining because it's so difficult, that seems like a recipe for disaster when closing the knife.