The real answer is probably both.
I will say this, though, it seems to grow more potent as you get older. This makes sense, as you have longer to look back, and more chances to trigger that nostalgia. I find this is especially true of music, since I probably bought more music in my 20s than at any other point in my life. I was in my 20s from 1984 to 1994, so the music of that era can send me off in a reverie pretty quickly1Excluding excessively cheesy synths and that weird snap drum sound that sounds extremely 19080s now.. Also, this decade saw the rise of rap, hip hop, grunge and R.E.M. probably my favourite band.
I may have more on this later. In the meantime, have a cat:
