Good way to show him how good you are- and that he has a long way to go- Let his tyres down to around 35psi and get the brakes binding. By about the third trip out- you will have to do this just to keep him in sight.

My daughter did her first and only MTB race at 12. The 8 year old that raced with her is now up to national level in the Elite class. 10 years later