LOOK YOUNG AS POSSIBLE!
A few years ago, we had a player (freshman in HS) at an underclass event. I looked at his running times, velocity, etc. and he stuck out like a sore thumb. So I made it over to his next game. He really was a very good player. His parents walked up and started talking and they were very nice people. I even talked to the young kid after the game and he was exceptionally polite and intelligent.
So what could possibly be a problem... Well this young boy had a full (and I mean full) beard! A ninth grader, an exceptional athlete, probably about 5'9/155, and a FULL BEARD at an event with maybe a couple with some peach fuzz!
Maybe it wouldn't have much impact on some people, but it absolutely ruined my first impression of this nice kid and fine player.
We are used to seeing outstanding seniors in high school that hardly have to shave. How do you go about projecting a ninth grader that is sporting a full beard? Answer... You can't, you have to go by the old what you see is what you will get. What we saw was very good, but it would have left a better impression had this young man been clean shaven.
We see the little hairy chins, but full beards on a young kid just doesn't make you dream about how good he might end up being some day.
Actually the boy I'm talking about was a very talented high school player and plays DI baseball now. Problem is, he was actually that good as a ninth grader and hasn't really gotten a lot better except for maybe gaining strength.
Don't leave scouts with the impression that you are 25 years old when you are 16-17 years old. That is not going to help. That said, if you throw upper 90s, don't worry about it!
BTW, I don't really care if anyone follows the advice above. Heck, I might be completely wrong, once again.