On a recent project, the customer charged me with making a bike that I would be excited about riding when I was his age. Admittedly he does have a couple of years on me. But we are very very close to riding the same size frame. He had even bought an old bike that I had made for myself back in my Bilenky days, then subsequently sold, which was then sold again. It's now on it's third paint job, and still gets ridden regularly.
What we came up with was an Allroad type bike. Disc brakes and clearances for both 650x47b and 26x2.3" tires (as pictured), with fenders. Thinner gauge, small diameter tubing to keep the ride nice and supple. A PCD MTB crown (RIP) for a little sex appeal. Sunburst yellow powder with matching stem and sparkly purple decals. Throw on mounting points for some Nitto mini-racks and you've got yourself a fun little bike that's ready to go just about anywhere.
So yeah, If 60 year old me just got this bike, I'd be stoked.