I'm 35 and I've been feeling old since about 1999/2000, and I was only in my early 20s at the time. People thought I was nuts for feeling old, but I remember feeling like a geezer at the thought of "80s dress up days" at schools and workplaces. I wasn't even that much removed from teenage life back then, but I already started to feel old and alienated from the youth culture.
The 90s going old, hell it was expected. I remember telling myself in the early 2000s that it will really be bad when the 90s go old, the 80s were one thing, but the 90s, that's when I knew it would be terrible for people around my age. But I know kids who don't even know jack about 2002.
My nephew was watching Batman and Robin from 1997 (he was born in 1997) and he asked me if the movie was considered stupid "back in those days". I had to tell him that YES we all thought of Batman and Robin was totally stupid movie in 1997. But he actually thought the public must have loved it and thought the movie super cool but then the movie just grew stupider because it's 15-16 years older.