It is hard to think of Facebook as being a 'mature' brand but I guess that is what it is

According to the Guardian and eMarketer 

In 2018, 2.2 million 12- to 17-year-olds and 4.5 million 18- to 24-year-olds will regularly use Facebook in the UK, 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.

Pretty much the same thing seems to be happening in the US. 

Facebook was launched way back in 2014. A decade ago it had 145,000,000 users who will now be aged in their 30s.

Brands are omnipotent until they are not. When I first worked in New York and passed the Pan Am building I would never have thought that the brand could possibly disappear. It did.

I doubt if Facebook is going to disappear but it is going to have to get used to dealing with multiple ages of users and that is going to be mighty difficult. Dick Stroud