Talk to him. That usually works.
Flirting is never desperate. It just tell someone you find them attractive enough to give them the attention.
No, it's very usual that the guy is older.
Cleavage
Some signs that an older guy may like you could include paying extra attention to you, making an effort to engage in conversation, showing genuine interest in your life, or complimenting you. However, it's important to also consider cultural norms and boundaries when interpreting someone's behavior.
He doesn't have to be older.
A older guy because sperm is more developt and more stronger but it can vary it can also be the younger guy it is impossible to know
try to be nice, but don't pay attention
Put out
You just do it.
React like you are more mature for your age. Be comfortable around him and be cool. Attract his attention whenever possible. But don't behave as if you are desperate for him.
Grow dredlocks
Get nacked.