One thing I heard a charter operator counseling a person in your position is....

You should rent the boat, but place your son as "Captain" of record, so when he wanted to solo, he could with his friends.

Yes, I too was dumbfounded when I heard this advise.

Again, the charter companies are the least of your worries. Kids come in all shapes. Some are content with doing "bible study" all night, others are interested in other things In my little clutch I have one content with word search on the boat, the other is more interested in "other things"