Funny Old People Joke

There was a man and a woman in an old folks home. The man says to the woman, I bet you can't guess what age I am. The woman says I'll give it ago, but first pull down your pants, the man pulls down his , then the woman says pull down your underpants, so the man does. The she taps around down there :D and she says your 97. The man asks, how do you know that? The woman answers, because you told me yesterday