The broadening as people get older is probably associated with people making non-age-related friends in their workplaces and communities. And as the array of plots above suggests, by people’s mid-40s, there start to be secondary peaks at younger ages, presumably as people’s children become teenagers, and start using Facebook.
And we don’t just have to look at things like cluster diagrams, or even friend networks: we can dig almost arbitrarily deep. For example, we can analyze the aggregated text of posts people make on their Facebook walls, say classifying them by topics they talk about (this uses a natural-language classifier written in the Wolfram Language and trained using some large corpora):
Read the full paper here: http://blog.stephenwolfram.com/2013/04/data-science-of-the-facebook-world/#more-5350