Most Helpful Girl
Nope, pretty normal. You could have gone to high school at the same time, so not really that huge of an age gap. You're both of-age. She may have a bit more of her adult life established, but you can learn from that. Sounds fine to me.
Most Helpful Guy
Where are you? In the UK it's easier because you can both drink, drive, and do everything an adult can do. Elsewhere this isn't always the case.
What are both doing in your life right now? Dating an 18 year old at unversity is different from an 18 year old in the last year of school.