Transmasc

A point that I want to raise is that sometimes people who are trans don't necessarily want to present in a straightforwardly binary way.

To give an example of what I mean, I had a friend, who I met when she was presenting as a boy, in school. Whilst she liked hanging out with girls more, she was never much of a girly girl, in terms of her interests. For a couple years after she transitioned and began presenting as a woman (we were adults by this point), she spent a while dressing in a conventionally feminine way. She later said that this was probably in part due to how gatekeepy gender affirmation care services can be if you don't present in a straightforward manner. But also she said she was (in hindsight) trying to jump through hoops to be what she thought a woman should be.

Eventually, as she became more comfortable, she leaned into a more tomboyish aesthetic that suited her, and picked up old hobbies that she had dropped due to feeling too masculine. Someone very unkindly once told her "I don't see what the point of you transitioning was if you're just going to go back to where you started". This was a silly perspective, because her adopting a lightly more masculine presentation wasn't a regression, but progress. It's honestly analogous to how I, a cis woman, had a phase as a teenager where I hated all things pink and girly, but now have a more mature view, where I can engage in femininity in a more healthy manner. It's growth.

This is all to say that your son may identify as masc, but give him space to explore what that means for him. There might be times where he enjoys more stereotypically feminine pursuits or aesthetics, but this doesn't diminish his identity in any way. Terms that he prefers might change as he grows to understand himself better, but if you keep an open mind, you can be there with him for it.