I don't like this rule. It is never enforced and i think it should be removed. We have plenty of 12-14 year old boys on the server and most of them are not annoying at all. They contribute well and even warden sometimes on JB. We also have a few teenage girls on the server. a girl can be like 18 and still have a really squeaky voice, should they get muted? To clarify, I'm 21 and not a squeaker, but feel sorry for of the younger players here.
This rule only targets kids with high pitch voice aka the squeakers with annoying headache inducing voice. It does not target girls.
I think people often misunderstand "high-pitched" for "high tune" voice. The kids we have are fine most of the time, but go on Garry's Mod RP servers and you'll understand why this rule is here. As long as they don't squeak and hurt our ears it's fine. But anything that does like a very bad mic or high-pitched squeaky voice is a no go imo.