im 15, i start moto trials at 13, and started on a 200, once you get better your gonna need the power, i might go to a sherco 290, so once he gets bigger and better, hes most likely gonna have to sell the 125 to get a bigger bike, when thats a pain, so why not just get a big bike now instead of dealing with the hastle later?
IMO
dude, trust me, once you start moto and get into it, your gonna want to compete, at first i didnt, that was before i even got my bike, i got my bike, and i was all for competing, now ive moved up 4 classes in 2 years, when you ride in comps and ride with people, you learn sooo much! and honestly its a lot more fun
if/when you get a bike, good luck and have fun with it bro!!