"Age and Sex" joke

This young fellow was about to be married and was asking his grandfather about sex.
He asked how often you should have it.
His grandfather told him, "When you first get married, you want it all the time, and maybe you'll do it several times a day.
Later on, sex tapers off and you have it once a week or so.
Then, as you get older, you have sex maybe once a month.
When you get really old, you are lucky to have it once a year, like maybe on your anniversary."
The young fellow then asks his grandfather,
"Well, how about you and Grandma now?"
His grandfather replied,"Oh, we just have oral sex now."
"What's oral sex?" the young fellow asked.
"Well," Grandpa said, "she goes to bed in her bedroom and I go to bed in my bedroom.
She yells,'Screw You!'
and I holler back,'Screw You too!'"