I just cant get on with 24" wheels, but part of that reason id I have been used to 26" for 12 years now, I am sensetive to where wheels sit, how they spin and hop, the smaller wheels just react totally different to what I am used to. If he has no previous experience, then he can choose either. 24" is more bmxy and there are more frame choices. I recommend he tries one first though. Stan rides a 24 and he is over 6ft, so I don't think that will be a problem.