Ask HN: When is a startup no longer a startup?

I'm wondering if there's an official answer, as well as some sort of community lore about the topic. Specifically, is Facebook or Groupon still a startup? What's the cutoff for when a company exits its innocence and turns into a real company? Inspired by the "most inspirational startup of 2010" post, as well as Steve Blank's "Elves Leave Middle Earth" post.