im 14 and i have to ride a 125. i think its a fine idea for b class rider to be on a 125 as it will start making us ride with more technique an rely less on the power of the bike pulling us up howere i know a A class riders who are 6 foot plus and quite honeslty i cant sea a 125 pulling a 11 12 stone 6 footer up a 6 foot rock step