I heard this joke on tv a while back.
There are these two old people in a retirement home. The old lady asks the old man, "I bet can tell you your age by grabbing and tingling you nvts." The old man says, "No way!' Then the old lady says, "Yes I really can, let me just show you." The old man finally says "OK" and he pulls his pants down, and she starts grabbing, tingling, and squeezing the old man's nvts. After a while the old lady stops and says "You are 76". The old man looks at her with astonishment and asks her "How do you know I am 76" and she replies "I know because you told me yesterday."