I think given the nature of "Life Story," Peter will age normally. It would run contrary to the story's themes if he didn't. So the cover for "The 90's" issue is exactly what it seems--an older, less athletic Spider-Man compared to his younger days via the reflection.

If I had to guess? I'd say by the 90s he's been out of the game for a while, having retired to raise his children. So a little out of shape but maybe able to get back into the game if he works at it (though still slower than he once was, even in peak shape).