Why do some people act like being in your forties or fifties is ancient?

I saw a question here recently from a woman asking what there was to look forward to after she reached 40. I was like seriously?
I don't know if anyone else watches the TV show Survivor, but there was a guy on there who was 52 years old and the doctor had to treat him for heat exhaustion and he was yelling something like, "Doctor Joe brought this old pirate back from the dead!" Dude! You are 52, not 82. That guy still has a good 30 years left on him yet!
Am I missing something here? Do people sign up for the retirement home once they hit 40?