As many have said flying experience is not important but showing an interest in aviation is. As for age and time to command that many seem to be discussing here, this varies so much at BA that its very difficult to predict. When I joined at 34, having trained at 27, there were long haul guys who had been in the RHS for 20 years just getting their commands, admittedly in long haul. Because of an unusual situation at LGW, which incidentally may be repeating itself at the moment, a group of us got commands after a couple of years in the airline as not many were interested in moving to LGW.
I suppose what I'm trying to say is that its very difficult to forecast anything in this industry and especially at BA. The new widebody aircraft may initiate an expansion, world economic situation allowing. The return to regular retirements post the raising of the pension age may also do the same.
Good luck to all.