Funny Grannys

A group of grannies are sitting in the nursing home when an elderly man walks in.
One of the ladies shouted: "We want to bet we can tell your exact age"
The old man said 'No you can't, you silly old bats'
The grannies called: "Just drop your pants and jump up and down a few times"
Certain that they couldn't know his age he dropped his pants and shorts and started jumping up and down.
The grannies had him spin a few circles and then called: "Your 87 years old!"
The old man cried "Unbelievable, how could you possibly know that?"
With tears of laughter still running down their cheeks they cried "Because we came to your birthday party yesterday!"