I'm 24 and might have something on the horizon with an 18 yr old. And i'll be 25 before she's 19. She's legal and thats all that matter really.
age don't mean anything mate if you like her go for it, aslong as they are legal you've got nowt to be worried about.
id check her id just to b on the safe side and make sure shes not lying, you only look 17 anyway though so it dusnt matter