A Joke: Upcoming wedding

Two guys are talking about their boss's upcoming wedding. One says, "It's ridiculous, he's rich, but he's 93 years old, and she's just 26!
What kind of a wedding is that?" The other says,
"Well, we have a name for it in my family." "What do you call it?" "We call it a football wedding."
The first asks, "What's a football wedding?" The other says, "She's waiting for him to kick off!"

What does the last sentence mean?
What is funny about the Joke? Can you get it?