To be clear, I don't think what I am saying detracts from the authors point, I just find it plausible that specifically the dirt-bike related arrests/fines/probations were legitimate.
The author probably was not in a dirt-bike biker gang when he was a kid, as far as I know that phenomenon is new.
(And honestly, I am surprised that the police were able to catch any of them in the first place. Chasing them down city streets would be extremely dangerous...)