Growing up, I honestly didn't think about it much at at all. Back then, "trans" wasn't even really a word -- there was just "transsexual" and I didn't identify as such probably because I never saw a positive example... I remember Renee Richards, who looked like a man, and Wendy Carlos Williams, who looked like a man, oh and John Lithgow in Garp, so I never really thought that I was TS because I never wanted to look like a man...
So 99.9% of the time, I didn't think about it, which was lucky, because at least I wasn't actively dysphoric.
Flashforward to my early 30s, and I'm wearing skirts at Pagan events and playing around with a new name, and suddenly someone calls me a cross-dresser, so I look it up and I'm like, no, not really... but then I bumped into references to beard removal and that was very appealing... which led to TSRoadmap and Andrea James's stuff on electrolysis and facial surgery, and I'm all "holy crap, that's me!"
And then I thought about it constantly for over two years, through bottom surgery and dilation and starting to have sex, and then I got into an actual relationship without (ever) disclosing... I still thought about it constantly for another year or two, and then, finally, that background chatter in my head finally stopped. And I rarely thought about it (maybe 5 to 10 days out of a given year) until the past three months or so, when I decided to do some touching up on my body -- get some more hair removed, lose weight, consider hairline revision and maybe a BBL, which got me back on the boards and writing about my experiences. I now I'm thinking about it every day again.
This too shall pass.