What age is it to ride above a 500cc motorbike in UK?

Its more to do with power output than engine cc. But for an unrestricted 500cc+ it is: Two years after a full Class A licence is obtained. (so minimum age 19) if the licence was obtained on a bike of 33bhp and power to weight not exceeding 0.16kW/kg. Otherwise age 21 if DAS, follow the link.