My best friend from high school pursued a career with the Coast Guard. He was a little hesitant at first, but with little desire to go into huge debt for a college education, he joined. 25 years in now and he has lived in some very exotic locations, has learned things that corporations desire in mid to high level management, and could retire today with a comfortable living ahead of him. He is 44 years old. The Coast Guard wants him to stay in and at this point he says there is no reason to leave the Coast Guard. He makes a very comfortable living and can retire at 50 with something to leave his son and wife.
It's hard for younger kids to see the future and most do not understand the value of vision. Understanding the value of the benefits that come in the future from this type of decision/career are sometimes invaluable. He did not get a college degree and he told me that entering the Coast Guard as an officer would have put him 20 to 30% ahead of where he is now. Also the risk of combat presence isn't near as prevalent as it is in the other armed forces. Obviously there is still risk, but not as much.
There are far worse decisions to be made for a young man of his age. Also, play as much football as he can. One day he won't be able to and he's gonna miss it. Speaking from experience here.
Good Luck!