I know my high school experience wasn't the greatest of my life. I was in a state of angst up to transferring to a new school in 11th grade, and had no friends for the first 3 months there. But since then, time has passed. I sat looking back at the experience with a sense of...not nostalgia.
Nostalgia is a feeling on the surface. What I got was something so much deeper. Reading the comments people had written, I began to embody the self I was in the 1990's. This dusty part of my memory was like one of the boxes, just waiting there for me to delve into. I've gotten this kind of memory before. Every memory has its own distinct flavor, and I could taste what it felt like to be that kid. It was refreshing. I began at once to want to go running, and to do ridiculous amounts of math.
So I can see why people sigh longingly over their high school years. I think some part of my brain has transferred all these memories into a 'good' folder. Egocentrically, I can say 'this is part of what made ME, so of course it's good.' However, even stuff I went through 2 years ago, or 6 months ago, have their own memory-taste. Call it place-ness or once-ness...whatever. I am not in the best place I've ever been in my life (I mean it's okay...), yet I expect the overall sensations of this moment will seem good when I look back on them 10 years from now.