Bike for bad knees, at least at first. Running does help the knees and if you're skinny enough you can do that. I'm personally a big dude slimming and I bike/ruck. Calisthenics for the rest. I'm getting old and my powerlifting days are behind me.
A bell curve for skills. Linear for combat (d20 or % roll high or low). I don't think a bell curve feels right for combat, which makes me odd man out if I want a simple single die mechanic rpg. Thankfully, multiple mechanics works fine for me.
Tunnels & Trolls was my first non-D&D game. I played it with some friends for a couple months before the GM moved away. Later on RQ3 became my go to game, which in many ways it still is. I can only handle an occasional foray into D&D of any sort. Ablative and escalating HP destroy my suspension...
This is one reason I mostly play Runequest or Harnmaster. Death can come at any time.
Alas, my games are heavy role-play without much combat, which came as a relief after years of D&D and players always looking for a fight.
I used to GM for a group using Warp World with my fantasy setting. It's complex, but I don't think it's the toughest game I've ran. Combat does slow things down and I don't like that much anymore. I want combat quick and out of the way.