In one hand I want to say good luck and just go with the flow. Life is way too short to be questioning everything. If she makes you happy, and vice versa then go for it.
Me, I'm 42 .....we are similar in age.
As a friend I am going to give some advice which is impartial.
Be wary. Society is less than accepting of such relationships. No, that should no be an issue, but be realistic.
One slight mistake or misjudgement and you could be in trouble. Please make sure she is 18, take absolutely no chances on that.
Leave no question marks over anything. And I am simply thinking of you in all of that.
My reason is, as a 42 year old guy, you have a lot to lose.
She as an 18 year old girl has much less risk.
If all is good, and above board, I would simply have some fun, and see where things go. Older men are attractive to younger girls, in some circumstances. So you wont be the first or last on that score. But I knw I would want to have something stable if I met someone now? And I feel an 18 year old girl wont want that heavy relationship.
There is no right or wrong, only you yourself know that. But make sure you are protecting yourself. I worry you are slightly leaving yourself open here.
Hope your ok?
That sounded a bit sad at the end.....being honest I wish I had the problem of younger attractive girls beig interested in me! I'm single and invisible to all women! 42 and my days are over