Can an 18 year old guy and a 23 year old guy make a relationship work?

you hit the nail right on the head. "Make" is the keyword. Five years age difference is nothing. Being away for a long time is going to be a big drag but if you make it so, it can still go, go, go. Try it out, for gawd's sake and have a fun time. After all, there is nothing to lose, is there?