How old is it? from this picture, I would say it is a hen because it doesn't have the big comb on its head, In the picture i have attached you can see that this rooster has a big comb and yours doesn't so I would say your safe to say it's a hen.
Looks like a roo to me. Looks to have the same sized comb and wattle as mine, he looks younger too. Also kind of looks like he's getting the 'spiked' crest that roosters get. Not all silkie roosters get huge combs, it's preferred that they have smaller sized ones.