You're a cool guy and a developing tennis player, I hope all the best for you.
World record for 100 meters is around 9.3
In junior high, I never ran slower than 10.8. Of course, I was a longjumper, 90's and varsity basketball, and 8th grade baseball player for my school.
Relax, flow, have FUN when playing tennis with your buds, which might be different in serious match play in tournaments.