From about 13 (when I first really became conscious of appearance) to 27, I dressed to disappear. Blue or black jeans, hiking style boots (I have wide feet, and boots are more likely to have generous width than shoes are. harder wearing, too), a plain grey or black t-shirt and a plaid or check shirt. Vaguely sort of 90s grunge/indie. My hair went crazy curly when I hit adolescence, and I'd wear a baseball cap in the summer or knitted/beanie in the winter to hide it til I was 19, at which point I tried (and succeeded) growing my hair about shoulder length instead. Grew a crap beard, too.
I wasn't exactly Guy Incognito (particularly as fashion trends moved on and I didn't), but I didn't stand out, which is what I wanted.
Then when I was 26, I started getting fed up with a lot of things about my life, including how I dressed. I'd long had an interest in styles ranging from about 1870 to the 1950s. I didn't want to dress exactly as though from a given period (not that I'd object if whoever did the wardrobe on Penny Dreadful threw some things my way...), but to take what I liked and try and put it together. So, cut my hair short, waistcoats and ties and nice shirts and smart/formal trousers, etc. I went through two fedoras before not being able to handle the 'Nice Guy'/'m'lady' associations (if only in my head) so moved on to a Homburg. Shoes wide enough but also with something in the way of style are probably the hardest thing. Thanks to charity shops and ebay, it's doable (though not always easily) on a budget. Browns and greens, and charcoals and slates and burgundies. Houndstooth, corduroy, moleskin. It's been a fair bit of trial and error, but I'm getting there.
As to autistic influence, I was assessed and diagnosed when I was 31-32, and my dress ('like an Edwardian gentleman', it says in my report) was taken as part of the evidence. I've come to understand a bit more about fabrics, too, that some are nicer than others - who knew! I am most at ease in softer cottons, and don't want polyester against my skin (though some poly-cotton mixes can be nice). I've had wool mix trousers that seemed to be made of fire ants, and wool mix trousers that were heavenly. I couldn't figure it out - there was minimal difference in the fabric composition.
Plus, around the house, it all gets a bit slovenly. Comfy pyjama-esque trousers, t-shirts and cardigans a-go-go.
The (perhaps) weird thing is, I'd swear I still don't want to be noticed, to stand out. It's both how I want to look, to present myself to the world, and something of a costume/armour (which I think explains why I'm fine with a shirt and waistcoat, but not a t-shirt and jumper). If people notice, they notice the clothes, not me. I don't know if that makes sense.
I've come to realise I'm going have to start wearing sunglasses a lot more - I don't know if it's gotten worse with age, or that I'm now aware it's actually a thing, but my light sensitivity is more noticeable to me. Oddly, it's easier on clear sunny days. Because I know where the light is, and it turns the colours up, and squinting tends to work. But those days where it's bright out but white cloud from horizon to horizon, where the light seems to have a weird, diffused, milky quality - that really messes with me.
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Of course, it's probably quite a bit more complicated than that.
You know sometimes, between the dames and the horses, I don't even know why I put my hat on.