You mentioned that you would edc it before handing down, which is awesome! Buck is a great heirloom tradition, but the 505 knight is a tiny little thing, just shy of 2".
The 110 can be a little big for some folks at 3.75" blade.
Ultimately your choice, but I would suggest upgrading to the the 501 (2.75") or the 112 (3") for a better edc size for you, a grown man... Go through the Buck custom shop and maybe upgrade to s30v Steel and go with a walnut handle, still remaining under $100, (maybe even have it engraved?), and use it, edc it, let him see you use it, and buy him his own appropriate little beater knife(s) along the way as he learns to use and handle and maintain/sharpen knives properly
(knivesshipfree does a great kids 1st knife program with a small Buck Bantam)...
Then when the time is right, and he's ready for a "nice" knife, a young man, you'll be handing him a (young) "man" sized knife with a great blade steel, and not a key chain sized knife with an entry level 420hc blade...
Just a thought... Knowing what I know about knives today, I would prefer a "better" blade Steel upgrade over a stag handle upgrade, but I Definitely like the general idea though...