I must say that trying to get the visual of the escalator that can go both ways is hard to do but I do know you cannot judge the health of a person by his age or outside appearance.  Hopefully, the older man at the top of the escalator left the house as you did with a plan to get do his business with pain as you did.  Limited mobility people have more of a plan when heading out to get through a day while in the outside world.  Maybe it's just best to take your turn even if you think the other person is worse than you. They probably have a plan too and are on top of their situation.