Playing tennis over 40 could be quite challenging!
Please consider previous injuries like tennis elbow and known body weaknesses during warmup, try to keep a balanced body especially between antagonistic muscle pairs like hamstring/quads and biceps/triceps. Pick one or few exercises from the following list to optimize performance on the court. Suggest to do 12-15 reps with elastic bands/light weights then trust the process...

• Stretching movements every day
• Plank
• Back pull-apart with band, seated rows with band
• External/Internal rotator cuff rotation with band
• Dumbbell lateral raises for shoulders
• Forearms dumbbell hammer curl, palms-up wrist curl
• Squats
• Calf raises
• Sprint intervals and jumping at the track
• Stationary cycling bike
• Walk the rest days