You are an idiot. When you're fifteen looking back on when you were right you'd realise in comparison you were an idiot. When you're twenty looking back on fifteen you'd think the same. When you're forty looking back on twenty you'd think the same. We grow, or at least should grow, to an extent that the person we look back on is not at all on our current level. So why would we want someone else who was on that level? Someone who is like that idiot?
Unless the person you are isn't growing or the person you're dating grew so much faster than you could ever have hope to then it's going to be an unbalanced relationship with someone much younger. It's why I very much doubt I could date someone of highschool age; so many things about their lives seem trivial and I feel like a parent when they offload.
As for being in a relationship with someone older, it's fine but if it goes too far then I become aware of the imbalances. I remember there was this guy who seemed interested in me, he was thirtyish, and he had so much more money than me so if we ever went to do something he was interested in then he'd have to foot the bill for me. Whenever we spoke, if I shared an experience and he responded with one of his one, it was far enough away that it felt like the times when my mother would tell me stories of the family when I was a child. His expectations of a relationship were also very different, can you say U-haul?
It was really disturbing for me and I didn't want to be around him but similarly, if he wasn't that much beyond me then I'd question why. I don't want to be racing ahead of someone who's that much older than me ... it feels bad enough with me handling things better than my older sister. I'd just pity him and be frustrated.
Summary: It's really weird to date someone a decade older, or even more, as an age gap when you're at my age. It's equally creepy to date someone who's comparatively sucking their thumbs at highschool too.