"I think that Facebook has pretty much reached a saturation point with young people. There just aren't that many more young Internet users out there who aren't on Facebook," said Debra Aho Williamson, a senior analyst with New York City-based research firm eMarketer.
She said it makes complete sense that Baby Boomers and Gen X-ers would be growing more substantially than other demographics on Facebook.
"It really represents to me that the way people are communicating -- not just young people -- is changing," she said.
Keith Loomer, a 56-year-old from North Conway, N.H., has been at the Facebook way of communicating for only three weeks.
After hearing about it from friends, he decided to see for himself what the buzz was all about. For him, Facebook has been a nonstop walk down memory lane.
He's accumulated a couple dozen friends (though he said "he's gaining them all the time") and those digital connections have stirred up memories of places he hasn't lived for years.
"It seems like when you get to a certain age, you start looking back at where you came from," he said, adding that he's had the most fun finding old friends -- even old girlfriends -- on Facebook.
"The amazing part is how people change. Everyone gets older, but you don't realize how old you've gotten until you see everyone else and go 'wow.'"
Beverly Meyer, a 61-year-old from San Francisco who joined in February, said it started as a way to share photographs but has ballooned into much more.
"It's kind of like going down the rabbit hole for Alice in Wonderland," she said. The more time you spend on it, the more it reveals its potential."
After about five months on the site, Meyer updates her status when inspiration strikes and uses it to keep in touch with far-flung friends from Greece to the United Kingdom to India.
Like others, she's found old friends and classmates. One childhood friend, with whom she had a falling out about three years ago, used Facebook to extend something of an olive branch and reconnect, she said.
Those who have been on Facebook for longer have an even more intimate relationship with it.
"To me, Facebook is like my sidekick," said Melinda, a 57-year-old New Yorker who asked to withhold her last name to protect her privacy. Daily she takes in the wisdom of the crowds, reading friends' updates and queries, and often contributes comments of her own.
For her generation, she believes Facebook provides companionship, optimism and maybe an escape from the foibles and frailties that emerge later in life.
"It's more than a playground. It's like going back to school -- to the community you had in the dorm," she said. And though that regression to a more juvenile time can also ignite more juvenile fears (who hasn't worried at least once that a fellow Facebooker might reject your invitation for friendship?), she said the difference is that online you are only as vulnerable and exposed as you want to be.
"You have a lot within your control, and I think ultimately that's a big thing for people over 55," she said.
But though boomers and those older say Facebook is good for them, some have asked if they are good for Facebook. If marketers want younger users who are still establishing their brand preferences, analysts wonder what happens if older members drive them away.