Waah really want tweety to be a SHE haha. About 5 months I believe. The guy said to expect laying sometime mid winter and assured that it was a pullet.... If it helps he/she is a very affectionate chicken and all the other chickens (hens) pick on him. He is very submissive to them.
IF the bird is in fact 5 months old, I'd say pullet - honestly, I would suggest you just hold onto him/her and decide when the bird lays or crows, you can always re-home him if he is a he, but would hate to see you get rid of a her by mistake. This one photo is one that could go either way really, do you have any other photos?
At 5 months old, I would expect to see a larger comb on a male... Could you post a few more photos from different angles? I agree that it looks a bit like a cockerel in this photo, but I'm not 100% sure. It seems to have some pullety characteristics too.