Lol putting it bluntly there.
But yeah, you can't consent to intercourse until you're 16 years old in most countries (apparently it's 18 in a lot of US states though, but that's irrelevant here). So if you do have sex and you either get caught, or she for some reason cries rape then basically you are VERY fucked, especially since you're 18+ so you'd be tried as an adult obviously. Though to be honest the amount of people who you hear of losing their virginity before they're legal you wonder how the fuck people actually get caught in the first place.
Age gaps become less of an issue the older you get, there's 12 years between my Mum and Dad, fine now, but that wouldn't work if my Dad was 18, my Mum would only be 6 years old!
So yeah, it's not a problem but some people would frown upon it at the moment. Things sound weird when she's still at school and you've finished etc.