As you get older, of course, you will not see the ball as well and you will not be as fast as you use to be. Are you going to get faster? No! Should you quit? No!
 
What to do? Try to start moving your feet in a slight left to right rocking motion before the point starts. You have not committed to a direction yet, but you are getting your body ready to react. Also, try to constantly be moving and adjusting your position every time the ball is struck. Remember, you are also trying to get aerobic and fit.
 
If you stand still too long, it is very hard to get moving gain. Once your body starts moving it is much easier to react. Sometime when you are playing a doubles match, count the number of small steps you take even when you do not get to hit the ball. You will find that you should be taking a minimum of a dozen steps even when you are not hitting a ball. Force yourself to go to the ball. Quit waiting! If you donŐt move you lose! One of the most common complaints I get from my students is "their partner does not move."
 
Have a good time on the courts!