How heavy/tall/old are you? If you're 16 or over you can ride any bike in a competition, and a 125 will quickly get too small and weedy for you. The ones I've ridden had no torque at all, you need to rev them to death to get them to go anywhere. I'd say get an older bike like a Yamaha TY250 monoshock first, I've had them for the last 5 years and they are dirt cheap to run and they're really strong, so you can fall off them a lot and not worry too much about breaking something. If you're old enough to avoid a 125, I'd say get a bigger bike definately, people will say, "ooh, they're fine to learn on,", but really what you want is to have fun, and while I found I could do must stuff on the 125s I rode, it pissed me off constantly.