Cannon law requires all bishops to submit the letter when they turn 75, but the pope does not have to accept the resignation.
"He'll accept it whenever he wants to accept it," the cardinal said.
Many Chicago Catholics would like to see Cardinal George continue as archbishop. Parishioners at St. Linus in southwest suburban Oak Lawn celebrated Mass and the cardinal's big day Sunday.
"He is an amazing man," said parishioner Susan Scardina. "Hopefully he wont retire soon."
"You are now looking at the oldest archbishop of Chicago, and the secret is pure stubbornness," the cardinal joked.
Cardinal George's so-called stubbornness has proved controversial at times during his 15 years as archbishop. Most recently, he took heat for using the Ku Klux Klan as an analogy when talking about the gay rights movement.
The cardinal has apologized for his words.
"I think I used a bad analogy. I hurt people, and for that I'm sincerely sorry," Cardinal George said.
"He needs to reach out. Let's see if we can find common ground here," said Joe Murray of Rainbow Sash.
Cardinal George does not have any public celebrations planned for his birthday Monday.
<>He says he will travel to Rome to meet with the pope next month on an unrelated issue, but he will bring up the retirement topic at that time.