I think it best if he got a non powered bicycle. On 2nd view, I think it is non-powered. Looks odd.
It's incredibly easy to get up to impressive speeds even with just a pedal bike, especially if you are going down a hill. It doesn't shock me at all that he got that fast, powered or not. I recall as a kid, using a bungee cord, tied to the seat post of my friend's bike, to get a slingshot boost on my skateboard. They would pedal as hard as they could (which at 12 is pretty damn hard let me tell you, we had legs like steel from all that pedaling) , I would follow behind on my board, holding the cord, and we'd take off on a downhill road in our neighborhood. I'd then pull as hard as I could for extra speed, and go rocketing off at truly stupid speeds for someone on a board and no protective equipment. I fucked up and got flung off the board one time, and I was going so fast, and the hill had enough of a slope, that I had enough hang time, to truly ponder how badly it was going to fucking hurt when I hit the pavement. And boy did it fucking hurt.
So yeah, kid deciding how fast he can go down a hill, fucking up and having a bad spill, totally in character, time honored tradition. Screaming in abject pain and fear at the solid smash, also time honored. I'm certain I've made similar sounds on...at least 3 occasions as a kid, from a serious spill.