This is 700,000 fewer than in 2017, as younger users defect to services such as Snapchat, according to eMarketer.
A surge in older users means over-55s will become the second-biggest demographic of Facebook users this year.
The report says that while Facebook has so far been successful in keeping hold of younger users shifting to services such as Instagram, which it bought in 2012 for $1bn, defectors are now increasingly heading to upstart Snapchat.
Facebook UK users 2018 v 2017
Age 12 to 17 2.2m, down 300,000
Age 18 to 24 4.5m, down 400,000
Age 25 to 34 7.2m, flat
Age 35 to 44 5.9m, flat
Age 45 to 54 5.6m, up 100,000 users
Age 55 to 64 3.5m, up 200,000 users
Age 65-plus 2.9m, up 300,000 users
In 2013, Rosabeth Moss Kanter Ernest L. Arbuckle professor of business at Harvard Business School said in the future, the biggest demographic change in the U.S. is the rise of the majority-minority.
In the Wall Street Journal she wrote that this is an odd concept that shows that we still haven’t gotten over the idea that white males are the norm and everyone else is a stranger.