UPDATE: After receiving information from Mashable about an even older user on Facebook, the company has walked back its claim that Florence Detlor is the oldest registered user. Read our full story here.

There are 955 million active users on Facebook — and not all of them are in their teens or 20s. The fastest-growing demographic on the service, for at least the last two years, has been women over 55.

And with that in mind, we invite you to meet the delightful Florence Detlor, 101 years young. According to Facebook, she has the distinction of being the service's oldest user. She's also the oldest person to visit Facebook HQ, where she met with COO Sheryl Sandberg, along with a guy young enough to be her great-grandchild: Mark Zuckerberg, CEO and founder.

Sandberg posted the above picture on her Timeline early Monday, along with the caption: "Honored to meet Florence Detlor, who at 101 years old is the oldest registered Facebook user. Thank you for visiting us Florence!"

The photo has garnered more than 5,000 Likes — and comments from users with 102 and 103-year-old grandparents, both eyeing Florence's title.

According to her profile, Florence graduated from Occidental College in 1932. She lives in Menlo Park — coincidentally enough, where Facebook is now headquartered — and is "looking for a good book to read." She joined Facebook three years ago this month, in August 2009.

[via AllFacebook]

Bonus: check out the sights of Facebook HQ, where Florence just got a tour.