Okay. She’s under 18. Got it. (Although it was already quite quite obvious, I just needed to make sure.)
If you’re under 18, you’re much more likely to be taken advantage of. When you’re under 18, four years is a BIG difference fundamentally. I’ve NEVER seen that turn out well. Most situations end with regret for the younger person.
If you don’t listen and go through with this…
DO NOT take action without telling your parents. Go by what they say. If they think its safe and okay, they’ll be able to take efforts to make it safe. If they don’t know about it because you haven’t told them, you could get yourself in a very dangerous situation, particularly psychologically. You are your parents responsibility until you turn 18. Let them protect you. If they say no, get over it and move on. Explain that its not a possibility without your parent’s consent and that you respect their opinion. You can do what you want once you’re an adult. There are still things that are inadvisable, but at least then it would be your own fault. I have seen this happen too many times to count. This is speaking from experience.
I doubt anything real will come of it. If you want a misguided fling, then do whatever. If you’re actually looking for a relationship, look somewhere else.