Many of my students, especially the older ones, tell me all the time, "I am too slow to play doubles." Typically, most players are not too slow. They have trained themselves to give up too soon. I estimate that a player in doubles can reach 80% of all shots in three steps or less. As you get older, you must get smarter. If a team can hit many balls where you cannot even touch them, you are probably giving them too many angles or you are hitting the ball too high. If you hit an angle return, you must be able to return an angle. In order to stop this from happening, hit more balls through the middle of the court. This will take away your opponents chances to hit angles.
Everyone has their own weaknesses. A universal weakness is failing to cover balls that go over your head. This is not fun for your partner. Take three steps to the ball before giving up. You will be surprised what you can hit. If you are at the net and getting no action, start poaching. If you receive a very short ball, do not give up on it until you have taken three steps. Don't worry about the balls you cannot get to. Worry about the ones you can get to. I believe that most players can see themselves being fast for three steps.
Get smarter, do not give up so soon and take at least three steps to the ball.
Good luck on the courts!