Older men want younger women because they are young. Your developed but fresh - no sagging tits, no wrinkles, no cellulite. Your body hasn't suffered the trials of time that older women have (childbirth, weight gain, etc), it appealing.
Also, younger women tend to "idolize" older men. It's easy to mistaken their age for wisdom, and because they have the advantage of experience - it's easier to manipulate younger women who are naive.
Honestly, men feel their age as well, sometimes dating someone younger makes them feel younger or more virile than they have been before. I guess you can say it's a way to recapture their youth.
Personally I find it disturbing. Having a teenager in the house, I wouldn't be comfortable for my daughter to date a man old enough to be her father. I think young people should stick with young people - at least until the woman has enough experience under her belt to differentiate between a man who is genuinely interested in her and a man who is just preying on her youth. I've dated a man 20 years older than me, but I was in my mid 20's when I did it.
Whatever the case is, a coach or teacher hitting on their students is wrong wrong wrong to me. There is a relationship established already and for them to take advantage of that to gain a sexual relationship with you is immoral and wrong. I think you should steer clear of older men until you are a fully developed woman mentally and emotionally.
Good luck and be smart. Their lives are almost over and yours has just begun. You have plenty of time to decide what type of men you prefer - no need to rush.