pkg-ages is a small program for Gentoo Linux that lets you see how long your currently-installed packages have been on your system. It doesn't parse your emerge.log file for a full installation history; there are other utilities like splat that do that. It is a command-line utility, written in Python.
If you have PyX installed, then it will generate a pretty little PDF histogram of your package ages. Otherwise, it just writes text output to your terminal.
Honestly, you shouldn't need it. But if you do, my contact information is in the file.
pkg-ages is Free Software licensed under the GNU GPL 2.