Personally Idon't consider long hair to be a sign of femininity, and neither do I believe long hair is a metal trait, although that's the popular belief.
Personally I have long hair and you should have guessed that I relate myself to metal as well, but when people say "hey you've got long hair, are you a metallist?", I usually cringe or get embarrassed, as answering "yes" would make unwanted stereotypes about me instantly, while a "no" would lead to me saying that I like "some of it" and the person I'm talking to would begin to talk about mainstream metal all of a sudden. I don't get dressed in leather, drunk, stoned and am not aggressive, but being stereotyped as a person "who is just the same as all other people who listen to "that type of music"" is something I hate.
Back to femininity, since when has long hair been a female only trait? The only reason why I can see this even being even taken into account scientifically is that females get bald much less often than males, yet this still makes shit sense. Sure, yeah, it is a tradition that women are long-haired usually and men are usually short-haired, but why should follow this tradition? However, something tells me that this is what I think simply because I *am* one of the long-haired men, and that's fucking it. The whole point is that long hair suits me better than short, I like being long-haired and that's the only fucking thing that matters! Of course, if I were bald, I'd look more manly, but then why would I want that?