Patience?
Everytime I play with old players I seem to lose, why?
I think the reason for that is quite simple; old players tend to have a lot more patience and experience in playing the game. Tennis is mostly hitting the next shot. When I play with those kind of players I try not to go for too much cause I know their game style and this would just fit their game. In my opinion, if your young you lack the same amount of patience, so why not use your strength! Which should be fitness!
I normally try to run my opponent down and let my fitness be the X-Factor!