Dirt biking first, you learn control and how to fall off/not fall off at slow enough speeds and (usually) soft(ish) ground so you don't hurt yourself too much. Then, once the skills have been learnt, possibly graduate to the track then road. I've been riding since the age of four, 48 years later I'm still alive, had a few accidents but the dirt learning saved my life or prevented my entry to a life threatening situation, more than once. An RS125 would be very high maintenance but gorgeous and he'd be the envy of his mates. But I completely understand your reticence. And I'm sure there are plenty more who'd agree with you.
