“Facebook is for old people,” I was told by a 17-year-old last week in San Francisco at the Startup Societies Summit. He doesn’t use the social media platform. He’s right too. About half a million fewer teens aged 12-17 will use Facebook this year compared to last year. Facebook depends on older people for its advertising revenue. But it needs to get users while they are young in order to keep them coming back to the social media website when they are older.