I think around 5 years older is ok.. I think it says a lot, generally, about older men who go after high school girls. Also depends on how young. It's still frowned upon though. Regardless, as long as laws about the age of consent are followed, that's your business. I'm not in high school, happy about it, and who you date isn't really high on my priority list.
And the whole "girls mature faster" thing is such a lazy, piss poor argument. Depends on your standards of maturity and what you think of what you hear that term as well.
I knew a ton of immature, stupid girls in high school, and I still know women like that today. I also know a lot of stupid, immature men my age and I'm Especially the ones I see going for high school girls. Also a lot of the time they have serious preconceived notions and try to manipulate the younger girls. When we were seniors, a friend of mine was going out with a much older guy. They were together for a couple years and when they broke up, she told me he was kind of abusive and the things she explained about his behavior sounded weird.
A while after they had already broken up, he sent her emails. She blocked his email and made another email to send her a final letter, mainly talking about how great he was and how she couldn't see that and is missing out. To make matters even worse and more creepy, he was her brothers best friend and watched her grow up. When I was in high school, I was usually more mature than most girls and I noticed the girls who went out with older guys were often not mature, thought it was cool that they were dating older guys and thought it was impressive that their boyfriends had money or cars and could get them liquor, several of them were the quiet, doormat types like my friend I just mentioned , etc.
I was never really impressed by it, but some other girls in school thought they were cool for it. Just observations, not saying all girls who go out with older men are that way. I'm sure a few genuinely connect with people. I still think child-adult relationships aren't the greatest ideas. However, our society and legal structure influences our ideas about what is right and wrong. You have to deal with that or build a time machine and go crazy on the 15 year olds in centuries past.
Good luck to ya. Do what you want, its your life. My parents definitely would. They don't even like the idea of me dating older men and I'm an adult.