Cosplay is a female-dominated hobby. In Japan, it's almost exclusively women who are into it. Among them, more women crossplay men than dress as female characters. This may be throwing the odds off a bit. I have seen male Lens though... even in Japan. There's even one on NicoNico who posts mediocre dance videos (though he's getting better, recently ~ go boy-Len! go!).
Generally speaking, women tend to make better little boys than men... they're smoother, slighter and prettier. Women have been playing young boys in the theater for centuries, and Len is voiced by a woman... like pretty much all of the other young boys in anime and games.
If you want to go for it ~ go for it. Your gender shouldn't deter you. People might even be MORE impressed that you're "accurate" down to the dangly bits.
But if you're still that worried about it ~ go for Kaito instead.