> others still need protection at 16

Other still need protection at 30, or in fact in my opinion also a lot of people above 50 (that didn't grow up with the internet around) are not prepared for what is out there. Also there are parents that are "underage". Those are not considered either.

I agree it is a very arbitrary limit indeed, but it seems there is no other good proxy so for a lot of people it will be choosing the best worst option, at least that is how the argument in favor is brought forward.