As a kid/teenager, I was hopelessly self-conscious, didn't fit in anywhere, and my confidence/sense of self was impacted significantly, so while I was particular about what I wore, I was never stylish and didn't have a great sense of self tied to external expression. (Plus, the self-conciousness made me want to be unnoticed, vs. drawing attention to myself)
I really only came into my own in college and into my 20's, up through today. In college I was probably more just focused on trying to look my best/attractive, with colors I thought worked for me. Same for today, but the difference is I have a better sense of what I like, and also am more apt to throw various things together (whereas in college I was still relying more on pre-packaged styles). I also dislike plain. I'm probably more dressy than casual, but probably more in a put-together sense, not a business sense. So if I wear a t-shirt, it'll be a fitted shirt, with a scarf, belt, earrings, whatnot... such that the overall vibe looks more dressy/chic than casual (I use the word 'chic' because someone called me that once in college, w/ reference to one of my jackets). I guess I'm a fan of simple but elegant/personal... so while I might wear a more neutral base layer (for ex., v-neck gray shirt) with jeans, I may have a belt over/around it, with a colorful scarf and larger earrings. Style/how I look's definitely not unimportant to me, iow. I place value in it/have fun with it.