All good questions. And with all due respect I would answer your questions with a couple questions that may eliminate some of your problems.

What kind of Kayak are you thinking about, where will it be used, (lake, river, ocean) and how big is your son? Has he done much paddling?

17 feet is a lot of boat for most big folks. I`m 6-2, 220# with 12-12.5 feet and my 17.5 is plenty of boat for me in the Atlantic Northeast. If your son were going to be using this boat, say, mostly in calm waters (a lake?) and he is a young man (average size teenager?) he may be happier with something a lot smaller.

Hope this helps. MBF