I took up mountain biking on dirt trails when I turned 70, but eventually the hills were just too much for me so I converted a hard tail mountain bike to a 1,000 watt E bike with a 52 volt, 14 amp battery (buying the motor and battery and replacing all of the standard drive parts (chain, gears, chainwheel, brakes, etc.) and now the hills are the easiest part. It was really a great experience doing the build, because I learned how to maintain and tune everything else on the bike. I can't ride the bike on paved streets since it can exceed 40 mph and is not legal on streets, but wouldn't ride on pavement anyway. Mostly, I ride blue and green dirt trails and sometimes black, but they invariably kick my a$$. Just an awesome sport being out in the woods, and seeing dear, fawns, fox, snakes, possums, wild turkeys, etc. Hard for me to relate to riding in any other environment.
Agree with you about tour riders. They are some of the most incredible athletes on the planet.