500 year old humans would look like a bag of sand poured into a transluencent non-water liquid in some sort of fish-bowl sized aquarium. Flowing around without a care in the world.

Because if they looked like old wrinkly people they'd be the meanest fucking people you'd ever dread meeting.

I definitely don't want to do 100 as a human, I could do 80 with a smile.. but I would not be surprised if I go far earlier since I don't trust your hell doctors at all.