Hi,
I agree with the above. I will, however, add a couple more points.
For any given infividual, transitioning at 17 is better than transitioning later in life. However, there are people who have an easier time passing than others, regardless of age. (I know cis women who get tagged as being trans.)
Second: Your size is a combination of predominantly three things: bone, muscle and fat. HRT will shrink muscle mass, diet and "redistribution" will shrink fat at the the shoulders. That 50 won't be 50 with diet, excercize and HRT. I know this from personal experience.
When a person transitions, it is because of what they are. If you are a woman with male parts, running out of fear from transitioning only works for do long. It will catch you again. There are legitimate reasons to delay transition. However, transitioning for any other reason than you are a woman is a very, very bad idea.
Wishing you luck!!
Hugs
Jen