Facebook was started in 2004, so it's a good 15 years old now. It also has 30,000 employees. That's way to big and way too old to be a startup in any meaningful sense. It's a big and powerful, but young, company.
By that standard, almost every company's cultural roots go back to a startup.
So, such a period would be a sensible time and place to look in an examination of cultural factors. The fact that Facebook is still young means that those roots are closer in time than for other companies and would seem to make that more relevant.