Is it illegal to date someone thats in his 20's im 15

i live in australia is it illegal?

Dating is okay, but not advisable. There's a problem when men want to date children. And you can deny it, but that's what you are. And when you proclaim your maturity, you are really telling us the opposite.
By the way, it usually involves sexual contact, not just intercourse. So any contact below the neck, and in some cases even kissing, is a no no.
. You may find yourself in a situation you are not ready to handle.
Depending on where you are, the age of consent is 16 or 17 in Oz. That includes for contact below the neck or sexual kissing.

I agree.

"Dating" could still be considered a crime because he would be encouraging a child to engage in sexual activities at some point. You are legally a child... and I agree with what dean0600 said. The more you say you're mature, the more adults know you aren't.

No, but if you have sex, he could be charged with rape and go to jail