The age restriction will vary depending on where it is that you are competing. Some places ask that you are at least 16 or 18, and some allow younger participants. There will definitely be somewhere your son can compete, so you should look around and see what there is near you.
Motorcross is competed in, all around the world, at various motorcross tracks
Well, you don't 'play' motorcross! You ride it, and you do this at any outdoor or indoor tracks.
Motorcross is popular EVERYWHERE but mostly i would say America and the UK
In the 1800s
no
British
well it depends on who but football players at an average do make more $ than motorcross bikers.
out of boredom, something different to do.
No, but thanks for asking.
ride dirtbikes?! lmfaoo.
falling down and death
about 70mph