Some people do have unlimited energy. Was watching a car show where this dude fabs up amazing shit on his own, and he only sleeps 3 hours a day, says thats all he needs amd he just wakes up and goes to play in his garage.
Some people just lucky. Then there's me, not old or out of shape, can sleep 13 hours easy and not have any energy, thyroid tested fine, im literally just a low energy person most of the time. Sucks.