AWKWARD ZOMBIE

I am in my late 40s, I play matches and hit 3-4 times a week and I want to stay/be in a good shape for playing with other fit players.

My overall shape is not bad, but I often play with guys who are lighter than I am and who play other sports on the side (e.g. soccer), and I feel I need to stay fit and stretched at all times in order to keep up.

My fitness routine, outside of hitting and playing matches frequently is to:

run 3x10 cross-court sprints from a baseline tickmark to the edges of the alley - different angles: run FH wide, run FH 45 degrees, run to the net, run to the BH 35 deg., run BH wide, and do this 10 times. It gets me pretty winded and my heart rate to 145. I repeat this three times. In between sprints, I hit 8-10 serves.
hit drills on a tennis ball machine, with lots of cross-court running

I feel this keeps me in decent shape, but I would not mind going further.

My questions:

Do you have a good stretching and conditioning routine to recommend that brings you and keeps you in a good competitive recreational shape? (morning and afternoon)
Do you have a good book or video to recommend?
What do you think about my routine?

In general many people are right, fitness has nothing to do with tennis and tennis. Still, an athlete at age 20 is not an athlete in as many years. Endurance is lost over the years, but muscles don't age. So in addition to sports, you can do strength exercises to give your body an energy boost. On the other hand, you feel your body better and understand when it's worth it to go on and when you have to stop. Take up personal development and try to explore new types of training. Find a diet for yourself and walk more often, simple walking will help to tone up your body, though many people underestimate this kind of workout.