I want to be a girl sometimes, is it normal?

I personally believe that this is not only not normal but also wrong. You say you are 16 years old, so I will base my opinion on that age. Such thoughts can haunt a person before and during puberty. But when a guy grows up and clearly understands who he is, there should be no such thoughts. The desire to be of the opposite gender is very dangerous, as its development can also lead to the development of pedophilia and homosexuality. Of course, if a person sometimes (very rarely) thinks about it, that is normal; it is inherent in everyone, but if it happens often, one should think about this problem and solve it. So, in general, I think that it is really stupid to live normally for 16 years and then start thinking that you should be a woman... It's idiotic... I think that's all. If you have any questions, ask.