My 16 yr old races these...but woods racing, not MX.
Started off on little 50 and moved up. He's fast as hell and no fear. Those 3 hour GNCC races are monsters...dangerous, rough and fast. We have had broken bones and hospital trips too.
He showed me a clip from his GoPro cam once...I almost **** and never looked at another one.
Best moment of race for me is when he crosses the finish line in one piece.
You might want to check out the Sprint-Enduro series ...