I might have posted about this before?
Or put it in a comment?
But I might as well write it again, since it has been on my mind.
I am 47. I often don't feel too old--its weird, sometimes I have relationships and activities that are a continuation of things that went on while I was a teenager. Sometimes I will think to myself about sharing in-jokes with my friends...who I might not have seen for 30 years.
But the one thing that really made me feel old is that there was a generation of pop culture that happened after I was an adult, but that is probably old to young people today. There are a lot of examples of this (Lady Gaga's first album came out 18 years ago!), but one of the biggest for me is the fandom culture of about 2010-2015. In 2012, when I was 33 and starting a job as a college professor, I started reading Homestuck. And got really into it. At the time, that was a fandom that was mostly older teens. I know that might be taken as weird, but I was just curious about a lot of these things that were popular on tumblr---Homestuck, Adventure Time, Gravity Falls, Welcome to Nightvale, Doctor Who, etc. (okay, obviously, the Doctor Who fandom existed long before tumblr!). I liked the attitude of the late Millenials, which was a lot more light and optimistic than the cynical Generation X that I had grown up with. Light, but also serious, in that I felt that younger people were more aware of the world in many ways. So as someone born in 1979, I kind of shifted my allegiance to Millenial culture, such as it was!
But I am kind of lost about what the popular culture even is today, and for a lot of young people---including people up to graduate school age, the internet and its vibes from 2010-2015 would now be before their time. So that is the one time I feel old, realizing that there are two steps after the pop culture I grew up with.