Even if we could guarantee that every player was over 13 we’d have standards of conduct. There is no way to ensure this, however.
I’ve had parents of children as young as kindergarten age email to complain about multiplayer conduct. It’s hard to say, diplomatically, that their child is too young to play online. I tend to recommend steps they can take to protect their child, i.e. put the device in airplane mode, and carefully check age ratings against the games they allow them to play, but even then I have many insist that it’s up to us to make online play with chat safe for their four year old. The world is a crazy place!