Years ago, the majority of cel collectors are guys; however
in the last decade or so, there're more female targeted anime series becoming more popular, like Sailor Moon and Fushigi Yuugi, so these shows attract a lot of female fans to start collecting cels.  Right now, there're still more guys collecting cels than girls, they are just not as vocal or like to show off their cels to the other collectors.  If you go to a cel related event in either Japan or US, there're still more male collectors than the female ones, but the gap is getting lesser nowaday, like 60/40 ratio.
As a male collector myself, I collect cels from female
targeted anime shows too :)