Oooooooooooo - You've got old U/C stuff? I told ya I regressed. I started with rubber free-flight (I was probably your age now). 3 kids, house, crap pay - and those kits are $10-20, give you a couple weeks of building fun then weeks of crashing fun
My wife, bless her blond soul, bought me a Goldberg Electra one Christmas, thinking it was a large electric free-flight. Heh - Christmas money and me: off to the hobby shop!!! That first kit-build (this was WAY before good ARF's), was a ball...no more teensy 1/16 balsa sticks, dope and tissue....nah - I'm on the kitchen counter with a 6.5' wing, her clothing iron and some clear Monokote...
After a dozen planes or so, I got the itch to try U/C. I built a Goldberg Whizard. Remember - NEVER bring your wife on a maiden flight of any kind. I had nobody to ask for help (this was also before easy Web access). The lines seemed kinda long "but if Goldberg says so, it must be OK". She held while I started. I run to the handle - "OK!! Let 'er go!". half-lap to take off, another half-lap with loose lines and me screaming,"Run away!! Run away!" It hit the pavement so hard it broke the cylinder off the trusty Cox.049.
*sigh* Being a diehard, I hied myself back to the LHS and bought a Fox .35 and Ringmaster. Taught myself to fly at the local Little League field, flying alone with a launching stooge of my own design. One thing led to another, and I've still got that Fox on a battle-scarred Sig Skyray and 4 Plastic Funtastics o- 2 1/2A and 2 .15's. If your dad wants to get back into U/C, these are the way to go. Absolutely indestructible flying wings made of foam and Coroplast. My boy, at 12, was looping on his 4th flight. (The fact that he was upwind in spite of my advice is neither here nor there - he can run fast). The 1/2A's are parts-drawer engines and the other two are a Fox .15 and an ancient McCoy .19 Redhead, both gotten off Ebay for like $15 total. I don't collect - I fly 'em.
The best advice you'll get is to go easy - start with a trainer and an instructor. Alternatively, start with a wee electric plane, no instructor, and be prepared to repair and spend more money. They're fear-inspiring when in the air.
When you're flying, you've got tunnel-vision. Remind me to tell you about float-flying one time. I was on my runabout, flying my Balsa USA Stik 40 off floats - fly flyf fly fly fly what fun - time to land, and I look around.....I had attracted a crowd of a dozen other boats or so - politely and evenly spaced for the cloest 1/4 mile in all directions.....I mean, I'm on a lake!!! I can land anywhere, right? *sigh* Yeesh.....