This is a good point, and my question as well. A TS may not know that what she has experienced all of her life was transsexuality, but at the same time this does not pop up out of the blue in middle age, after she has had a happy marriage, enjoyed being a father, and has otherwise led a successful male life? Surely, there must have been some dissatisfaction with being male for quite some years, for someone who feels that she was born in the wrong body? I'm asking because I don't understand late onset TS either ... although I do understand, through my SO, someone who is gender non-conforming.
Maybe some people can look back and instead acknowledge a long-standing form of depression, without pinpointing it to GID? But, in the interest of providing a point of view from someone who knows that she is not TS, and at the risk of posting too much in a public forum, I realize now that I've suffered from depression most of my life without being able to label it for what it was, not until my 40s. Still, I know in the deepest part of myself that it had absolutely nothing to do with any feelings of gender/sexual incongruity. I have always enjoyed my body bits.
I have also felt close to both men and women emotionally, have enjoyed doing things with both genders, have had male best friends with whom I could discuss anything, and have even enjoyed competing with men as a young woman when I was building my career. But, as a group my reptilian brain always saw men more as people to have sex with than seeing them as sitting on the same side of the fence as me.
This, I understand.