Not knowing what the current life circumstances are that are keeping you from transitioning, it's difficult to be very specific with regard to how to get started. (Is that even possible given that you say your current life circumstances make transition impossible?)

One good way to get started if you can, regardless of your current circumstances, would be to find, & get with, an experienced gender therapist. It is really important, from my perspective, to find someone who is interested in working with people who have gender identity issues, & who is both knowledgeable & experienced. A therapist who is not can do more harm than good in my opinion.

I'm 70 years old now. But my own gender identity issues go back to my earliest childhood, back before I even have anything in the way of reliable memories. There are at least one or two others, here on PC, who have struggled, or are struggling, with gender identity concerns of their own. They no doubt will be closer to your age than I am. But if you want to correspond with regard to this, via personal message, I'm available. Beyond that, are you on the Susan's Place website? I'm not a member. But it seems to be the premier website for people who are transitioning or who have gender identity concerns. If you're not a member, it may be worth checking out. My best wishes to you...