More power to you. Great set of athletic goals for your future.
I'm age 67, going on 107 I hope. I also have no cartilage in my knees, plus bone spurs, related to Army service in the seventies. The more I ride the bike the less the knees hurt. I ride a bike everywhere I don't rent a U-haul truck, and the constant use has since I quit working age 58 dropped 55 lb , pulled rest pulse down from 85 to 64, cloresterol down from 213 to 130.
A few tips. You live in the US. I wouldn't want a small wheel bike like the tern or Cero above. We get potholes and uneven pavement in the US, up to 6" deep and separators up to 3" high don't get repaired for months. You want at least 26" wheels, to cut shock when you hit an elevation change. I missed it and hit a 2" pavement ledge last Saturday at 8 mph on Louisville river bike path , and had to push the bike up steps when park dept. allowed vendors to set up tables on the ramped bike path. For comfort I prefer 1.75 " (45 mm) to 2.1" (55 mm) tires or bigger pressured only to 50 psi. That pressure keeps me from denting the wheel on a sidewalk ledge I go over weekly with groceries. I use Kenda Full knobby tires which are a bit noisy, but grip better if I slide over the pavement edge, and have 500 % fewer flats than the thin street tires I was riding previously. I don't ride a suspension bike. I do have seat springs. Many pro level bikes won't take tires that wide.
If you go over 15 mph in the wet down hill you'll probably want disk brakes instead of rim, which are less likely to fade due to being wet. You'll want an aluminum frame if you ever intend to put the bike on a bus rack. A short frame big wheel electric bike reviewed here is the izip p3 protour
https://electricbikereview.com/izip/e3-protour/
which has aluminum frame, disk brakes, turn back handlebar, a book rack, and comes in 3 sizes.
I ride 12 months a year, only falling back to riding the city bus to the grocery store when the city has pushed mounds of icy snow into piles in the bike lane & sidewalks. Black glare ice I won't ride on, but I will ride on snow up to 12" deep. I wear clothes to handle the temperatures. Extreme contractor grade gloves are required some times, available only at the farm supply or home store. I wear up to 5 layers some time, say 5 degrees F & below.
I need 21 speeds to get up 15% grades here in Clark Cty, including a 30:29 low low sprocket. Using that gear is slower than walking, but riding unloads my wrists & back twister muscles from pushing the bike. That is without electric assist. That means a triple front sprocket: 30, 42, and 52 sprockets, 29 to 14 on the rear. Bosch mid drive systems replace the front sprocket set with their own single, so IMHO they are not for pedal assist up steep hills.
See my current rides below. I carry up to 50 lb of groceries. Because of the uneven weight distribution this causes (85 lb rear 25 lb front without me or groceries) I'm looking at buying stretch rear cargo bikes like the yubabikes bodaboda
http://yubabikes.com/cargobikestore/boda-boda-v3-24-speed or the kona ute
(Link Removed - No Longer Exists)
xtracycle also has a long frame cargo bike.
You'd want the taller step-over bodaboda of course with your long legs. Or the large kona. As you can see from my pictures, my leg inseams are short, 28", my torso is long, so I'm riding upgraded kid bikes.
Best of luck shopping and achieving your fitness goals.
