Slice everything, keep everything low, and look for oportunities to get into the net. Slice serves....and even slice forehands are also very good tools to have as age catches up with your game.
Also learn an effective drop shot and a good deep lob (does not have to be topspin).
Try not to get into ball bashing contests with younger players who have not come face to face with age. Learn to keep the ball low and use angles and court positioning to keep more modern styles off balance while controling the pace of the point.
Also...hot baths before playing and lot of ice after are good practices.
Tennis is not an age friendly sport. If your a hard explosive mover I would suggest studying players like Edberg and McEnroe in terms of court movement.
Just some tips to try and keep you in the game longer. Playing doubles more will help with a lot of this as its more of a crafty shot makinging/placement game than singles which is more movement based. In this reguard doubles will make you a better singles player.