Why 20 to 40? I am 62, A PADI certified deep diver, mountain bike rider, and golfer.
In my spare time I do work on my 1996 GMC k1500 (just did all new Stainless Steel brake lines, brakes, brake booster, master cylinder, calipers and wheel cylinders, new distributor, cap, rotor, wires, may sensor, map sensor, crank sensor, coolant sensor, ignition module, injectors, fuel pump and sender unit (by tilting truck bed), added hid low beams, led bulbs, headlight bezels, tail light bezels.
I may not be hiker of the year but then I built my rear retaining wall solo, moved 40 tons of gravel in our drain field at 1.6 tons (avg) in my 1/2 ton k1500, painted the walls of my ranch style house solo, then walked my dog on Ragged Mountain behind my house. In the last 12 years.