I don’t know about the author of that quote, but I mentally often think of the 90s as “last decade”

Interesting. Is that a reason behind it? I can see why the 2000s might seem like "last decade" (it might still feel like the 2010s), but the 90s are another decade behind...

I don’t really know, but Y2K and 9/11 were fairly notable in a way that most of the other decade transitions weren’t.

I also don’t really know if this is common: but the individual years of my adult life just seem less real than my childhood for some reason.

Because the human brain perceives time in odd ways.

That joke was funny 10 years ago.

It's probably not a joke. Many people report things like this when talking about time. Our brains are just not that great at accurately thinking about long periods of time.

Clearly his directly outer conscience thinks it's the 2010s