One day at the rest home, an old man and woman are talking. Out of nowhere the woman says, "I can guess your age."
The man doesn't believe her, but tells her to go ahead and try.
"Pull down your pants," she says.
He doesn't understand but does it anyway. She inspects his rear end for a few minutes and then says, "You're 84 years old."
"That's amazing," the man says. "How did you know?"
"You told me yesterday."
Source: Sex jokes