It really depends on what level you are. I play in the Southern Connecticut division for my high school, and we are all around 3.5-4.5, varsity starters usually being 4.5+ for 1, 2 and 3 singles, and 4.0 for 4 and 5 singles and 1 & 2 doubles, and the kids on good teams usually serve high 80's or low 90's. the #1 singles player on our team serves 110 flat, and about 90 w/ kick and he is 17 and probably about 5'11 160lbs. I have the second fastest serve on the team and it clocks at about 95-98 mph on a first serve, usually mid 80s on a second. I dont hit a flat serve though, because I can never get it in so I dont know how fast it would be and it wouldnt really matter, speed is just an added bonus to a serve anyways, as you get more aces by placement than pure power