Agreed; I guess many of us will have a blind spot when it comes to recognizing our own minds aging, and our memories accreting into a golden history.

Seems to be a part of the human condition.

Time's arrow moves in one direction, the past cannot be reclaimed. The challenge is to not become bitter about it.

Yes, I've succumb lately to reminiscing on the halcyon days of the early web too. I happened to be a teen then, so the memories are fondly intertwined.

I recently learned the term reminiscence bump that it looks like some folks are also enjoying: https://en.wikipedia.org/wiki/Reminiscence_bump

Not just childhood, but I miss having that first-time experience for some of my (later) favourite activities.

Guess I have to try new things ... but what?

I thought so, too. There are still enough communities hosted on phpBB, there are still enough ways to tinker around, join IRC, find ridiculous geocities-like websites or whatever. It's more that people choose to use FB, YouTube, Reddit, Instagram.