[User23]

> If your oldest Facebook post is from 2015, how likely is it that you've been using the internet before 2005?!

Who knows. It could be that person has been using the Internet for a very long time and is thus a late adopter of Facebook due to preferring to do things the old way. It could also be a person who started using the Internet in 2015. GP's point that we really can't conclude anything beyond a lower bound isn't falsified by your example