This is difficult to explain without sounding condescending, but let me give it a try. When I was 14, I felt very mature. Most 14-year olds do. We start thinking about sex, about what we'd like the world to be like, about our own behaviour and that of others. But to a 24-year old, there are many differences between someone who is 14 and someone who is 24.

Someone who is 14 doesn't have the same experience with relationships as someone who is 24. To a healthy 24-year old, this is a negative thing. We learn about relationships by having them. A healthy and nice 24-year old wants to interact with someone who will not fall for old tricks and pitfalls. They want someone with the same level of experience. I'm not talking about sexual prowess here, but things such as knowing and protecting your own boundaries, respecting the boundaries of others, not being manipulative or getting manipulated, etc.

A 24-year old would never openly date or even flirt with a 14-year old. To understand why, imagine this scenario: would you want to be seen flirting with a 10-year old? What would you think if you found out a boy in your class was seeing a 10-year old girl? Would you think the girl must be cool for her age, or would you think there must be something wrong with your classmate?

That's what other people of 24+ think of guys who are dating girls who are that much younger. Not because those girls are not cool or cannot be good at sex, but because they wonder why that guy prefers a girl who is so much younger. There are manipulative flirting/dating tricks that don't work on 24-year old women anymore, because they've already seen them. Wouldn't you rather learn from those mistakes by having them with equally inexperienced guys who are roughly your age? There are guys who seem cool, but only if you don't know many other 24-year old guys. Wouldn't you rather be able to tell if you are seeing a good guy or someone who is only pretending to be a good guy?

Imagine what that 10-year old girl would feel like if she were dating your 14-year old classmate. She'd feel so cool, and she'd be proud of her boyfriend because he was so much bigger and stronger and more mature than her classmates. But you'd know he was fairly normal for his age, and now you think less of him because you wonder why he enjoys hanging out with a 10-year old. Does he like her adoration? That he knows more than her? Or maybe even that he can manipulate her into doing things because he knows things she doesn't?

I'm sure that you're a cool and fun girl. But don't feel flattered that this older guy noticed that you're great. Feel worried that he doesn't go for cool girls who are closer to his own age. Google the term 'grooming', you'll find lots of tricks that are being used by guys to lure naive (and often younger) girls into situations that they're not comfortable with. You're probably mature for your age, so why not find a guy who is also mature for his age instead of a mature guy who is emotionally stunted for his age?

Edit: I'm happy to report that I have received nothing but kindness and gold in response to this post. I am grateful for both. I hope the same positivity was extended to the OP of this thread, before she deleted her post. Asking questions about these topics is difficult but so important. Finally, I'd like to point out I'm a woman, as there seem to have been a few unfounded assumptions on this part.