Compared to my serve when I was playing in college my serve sucks. I had my friend who is a tennis pro give me a serve lesson. He said I have great technique but no flexibility in my shoulder. He had me setup in my racket drop position and he physically showed me where my arm drop was. where a pro has his forearm parallel to the ground (3pm) at the drop my forearm was about 1:00pm. Barely past vertical. So that is why my serve max mph is compromised. Old age sucks. He gently pushed on it to see how far I can rotate but it is basically stuck around 1pm.