scr1 is correct. The medical restrictions depend on the job he goes for. If the role requires an airside driving permit, the aerodrome operator/handling agent may put on restrictions that they deem fit ie allowed to drive on apron areas only.
If he will be using specialist equipment such as air bridges etc then there may also be some restrictions. Best thing to do is find a job he wants to go for and then contact the company well in advance of applying to get the information.