If there were 23 relationships that is indeed a red flag. But casual sex is not a relationship, no sin and no one should be condemned for that.

This points to another worrying trend I've seen among teenagers and 20-something people. I've often seen them commenting how they have had absolutely ridiculous amounts of relationships, like a 24 year old saying she has had 11 boyfriends.

It's like casual sex has become to prevalent that they think that's what a stable relationship is. I can't really fathom the logic.

You are extrapolating way too much from your limited data — in fact, younger generations have less sex than those before, as per a study linked in this thread.