prefferably the 85cc class
10- 15
everywhere
about as big as they always was
65cc 85cc supermini
up to approximately 120 pounds.
43 litres
85 cc or 150 cc
if he is just starting then 250 beg
No we can't use 100cc 4 -stroke dirt bike race against 85cc dirt bikes.
125 or 250 if you fit on the but but they run together in the 250 class
The following is from one of my local motocross tracks, most local tracks should have something similar: 0-85cc 7-15 Beginner 0-85cc 14-15 years 150cc and smaller 4 Stroke, 15 years old & younger
 and any of the novice or intermediate classes depending on their ability