Sometimes as I'm thinking back over my life, I'll realize good god, that was 15 years ago! Or worse, 25!
Some memories are so vivid that I get a little bit scared - feels as if I think too deeply about the past, I might POP! back to that point, and then I'd be stuck reliving all that stuff.
That's not to say reliving the good times wouldn't be fun, not that there wouldn't be opportunities to be had, but so much of it was boring.