Do you use the term 'son' when talking to him? Pronouns are as important to hear as nouns.
Hopefully it will help him realize you understand, more than just telling him you understand. (Hey son (not Hey Matt), want to go . . . )

He's at the age of not talking about his feelings, even if being trans was not a part of the equation.

Get him involved with guy things, if possible, and if you also do guy things. Working on your car, ballgames, etc.

And yes, tell him you are also trans in a way. Tell him you know what he is going through is a lot different than you being a CD. You can show him, if he asks to see, otherwise it is just something else he'll be confused about.