Uncle, Let's Get Married

They all say that the old men like to nibble on tender girls, but if she meets an old uncle who doesn't like nibbling on tender girl?  
"Uncle, let's have a date."
"I don't like the younger ones."
"Then, uncle, let's get a marriage certificate."
"A marriage certificate? Hurry up and read. If you don't work hard, you can't get your graduation certificate."