A 90cc are 125cc 4stroke
yz85 in two years yz125 or 250 if you are ready
a 120cc dirt bike is suitable for a 17 year old
dude a KX90 should be good
You Should get the Diamondback Overdrive
A dirt bike can range from 100-300 pounds. It all depends on the size of the engine, the large 530cc bikes will weigh the most while the small 50cc bike will weigh the least.
There are different sizes for dirt bike wheels as there are for regular bike wheels.
A 150 to a 250 honda. Motocross? maybe a 200cc
A 50cc dirt bike doesn't technically have a weight limit. There are many full grown adults weighing in excess of 200 pounds which own and ride dirt bikes of this engine size.
there are no age limits for dirt bike. but there are recomendations for size
probably a 250four stroke :)