The bug bit me late in life. I heavily repressed any aspects of my own gender non-conforming behavior or thoughts until after my parents were both passed away.
I think though that when I first realized I was hooked was when it dawned on me that on almost every trip through a store that sold clothes and shoes, I was staring wistfully at the ladies shoes and boots, and wishing I could wear shoes like those. They drew my gaze like a magnet! I couldn't care less about the mens' clothes, or the tools, or lots of other stuff. I hadn't even bought my first panties yet, but I could recognize the desire was there.