McEnroe is still fantastic. I would say he may be the GOAT in terms of longevity. He has not really lost that much since his retirement. The only other player that really impresses me in terms of movement is Edberg who still looks great.
It should be said that the way these players hit the ball and move transitions well higher ages. I cant see a player like Courier or Chang not falling off without a lot of training. They look pretty good as well though.
I almost forgot...Wilander is also very impressive....still moves great.