Similar here - mid-50's and 5.0, and in good shape, at least cardio wise. However where I feel my age most is on speed of recovery to neutral position between shots. Or more accurately, lack thereof.
Hit heavy into the corners against me and I will get to the ball... once or twice... but will end up giving up too much court. I've had to become more aggressive earlier in the points to compensate - take the initiative before my opponent can.
That's what's curious about the OP's opponent - mid 50's and a pusher/retriever is not a recipe for success IMO.
Yeah that would definitely be the way to play against me. If my opponent hits a good serve and then the +1 into the other corner, I can get there but can't recover back into the court fast enough.
My counter strategy is to gamble with being super aggressive on the return, hope I can get lucky and string a few together to break, and then focus on holding my own serve.