This is actually a toughy. I'm quite liberal when it comes to sexuality and what you identify as. I mean, I think it's ridiculous that some people identify as cats and wolves (damn furries
) but at the same time it's like 'if it makes you happy, you do you'.
That said, there is a shockingly high attempted suicide rate for transgenders (~41% according to some studies). However, whether this is due to societal discrimination, or regret/unhealthy psyche to begin with, I have no clue. I guess I'd be worried, I mean If my son goes through with this lifestyle,
he's opening himself up to bullying, trolling, ridicule, persecution and in some cases physical violence just for him being himself(herself?). I'd have quite a few long talks with my son, I'd listen, and understand where he is coming from, because nothing is worse as a child than your parents not understanding who you are, and forcing their views of who you should be on you. But (ready the pitchforks) I would try and dissuade him from the choice for a few years. Not actively forcing him into a 'manly' way of being, but encouraging him to find a middle ground where he is happy as his gender/in his own body, but also remains himself in personality and preferences.. if that makes any sense? Above all though, I'd be supportive of him and his decisions.
There's a quote I like alot that answers why I'd be so supportive, to paraphrase it "when we try and be someone we are not, either we succeed and feel as we have lost ourselves, or we fail. Either way, we despair. (So be yourself)" Really not doing the quote justice
. Doesn't mean you can't try and improve, or try and fit into societal norms abit better. But above all you shouldn't change what fundamentally makes you, you, to achieve that, because you'll be more miserable if you do, than if you go against the grain of what society deems 'acceptable'.
Ofc it's hard to give a real reaction when so much of the scenario is left to the imagination, like whether he wants gender-reassignment surgery or not, but the above is just how I'd react to the general situation at first.