Nothing signifies social networking more than Facebook, the dominant platform for users in the United States and the choice of 71 percent of online adults last year, although not to the exclusion of other sites. That’s up from 67 percent a year earlier.

Where is this growth coming from? According to new data from the Pew Center for Internet and American Life, the answer is: computer users over 65. That’s a significant generational shift.

Until recently, Facebook was synonymous with a youthful communications revolution. It was hatched at Harvard University; its billionaire founder, Mark Zuckerberg, is not yet 30.

The report says that 45 percent of Internet users 65 or older use Facebook, up from 35 percent in 2012. It is especially popular among older women.

Meanwhile, the percentage of those between the ages of 18 and 29 who use Facebook fell 2 percentage points last year. They are gravitating to other sites.

All of this may be a surprise, but it tracks with age-old trends that predate the Internet. What is cool with younger people doesn’t stay cool forever. At the same time, Facebook is a boon to parents and grandparents who now have quick access to family photos and news once delivered in letters by the mail.

Facebook will be around for a long time. But the new data prove some things we already knew: Technology is inherently dynamic, and the only certainty is more change.