I'm going to work on a more detailed version of this post-- winning %s, particularly low ranked victories, and I'll try the age thing (though that might take a little longer). I'll need a few days though.
I have other statistics, I hope that you serve
1988: Roger Smith (nº150) defeated Ivan Lendl (Nº1)
Becker defeated 6 differents Nº1: Lendl, Wilander, Edberg, Courier, Sampras and Agassi
1996: Thomas Muster lost his first 3 matches as Nº1
1999: Patrick Rafter was Nº1 but never played a match as Nº1
2001: Gustavo Kürten and Marat Safin lost 5 matches in a row as Nº1
But I haven't age statistics