Be Prepared To Suffer the Consequences
I would find it hard to imagine how much an 18 year old and a 38 year old could possibly have in common that, in the long run, would be able to build the foundation for a romantic relationship.
If you are looking to just get some action because you have a crush, then you have to be willing to suffer the long term consequences of your decisions.
Getting involved with a 38 year old could most definitely mean that expectations on his side may be more than what you are ready or able to handle. Where he is in life and where you are in life are two very different places and the chances that anything more than a physical attraction is really there may be slim.
Only a Few Common Interests
Granted, you may find him to be a great guy with a lot to offer who is very supportive of you and whose company you enjoy. The reality is that may be where the "things in common" end. I would not advise pursuing this guy when you graduate. The complications that may be involved as far as your parents, the people in the community, your friends, and within yourself may not be worth satisfying an urge.
Age Difference Too Big
I think the age difference is too big and that the cons would outweigh the pros in this situation. You have managed to abstain for this long I would recommend sticking with that idea. That way the relationship that you have now can be maintained without suffering from other possible bumps in the road as a result of a different path taken.
Good luck and whatever you decide to do, think carefully and be safe.