> My dress shirts are 20-30 years old. They're not out of style.

They are, you just don't care. Which is OK.

Eh, you can pick plain white or blue button-up shirts with one of a few normal collar types and you won't be trendy but you also won't be "out of style". There are also some approaches to fashion the point of which is (at least in part) that they change only very slowly ("prep", for instance, which is practically defined by that quality—certain very casual styles like country/cowboy might also qualify, they have trends but you can definitely avoid them and achieve a look that's as close to timeless as it gets, on human-lifespan timescales).

Suits are slowly evolving fewer buttons but you're probably still OK with a 3-button in most contexts, and a 2 or 3-roll-2 is probably future-safe for 15 years at least. Suits may well be almost gone by the time they're out of fashion, really, and will only remain in contexts that don't really evolve (the 3-button is firmly OK in a legal, funeral, or wedding context, for instance, and likely to remain so pretty much indefinitely, provided, in the latter case, it's not an extremely formal wedding and/or you're not in the wedding party itself)

You're right that I don't care, but if you saw a photo of me in one you couldn't tell what decade it is from.

Classics never go out of style.

I'm kind of in the same boat. I never cared about fashion much. It always seemed hollow and vapid to me. Even as a kid/teen-ager/20s when it's supposed to matter the most.

Perhaps your circle of friends didn't care either.

For kids/teenagers/early-20s, what matters is belonging - observable patterns of behavior that follow are whatever gets amplified when everyone looks at everyone else in their vicinity for signals of approval.

FWIW, I also didn't care about fashion, and neither did my friends. I expect this to be the case with quite a lot of HNers - this comes from being a nerd and having nerd friends. We amplified each other on different patterns of behavior.