I was diagnosed late in life, when I was 40. I lived my life passing as "normal" and while I certainly struggled, I was completely oblivious to the fact that I am autistic. My wife knew all along, and it was with her help that I got diagnosed. At first, I resisted the diagnosis. But over time, as I looked back on my life and looked at my struggles and compared them to autistic behaviors I realized the diagnosis was correct. I have since learned to live with myself with this new information, and my quality of life has certainly improved.
I think imposter syndrome is a normal thing, for everybody. I know exactly what you mean about "faking it." I often felt that way in the first few years following my diagnosis. But, I also know it isn't easy to get an ASD diagnosis. Somebody had to see something in you to say, hey let's get you to see a professional. The evaluation is then pretty intense - at least it was for me. There is also no way to monetize ASD as there are no medications or treatments available so diagnosis aren't given out as much as others where they can sell you meds.
I guess I am trying to say you aren't alone in your feelings. I hope this helps you to feel some comfort!
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