There seems to be quite a lot of inconsistency. On my last HNL flight I was able to request an exit row online on a 763, but shortly after that I was told when I was going to LHR that the seats were held until check-in. Curiously, on my way back from TPA recently, I was just in front of the exit row that had two older people who did not seem to fit the able-bodied category as well as I would have liked if there had been a problem.