This is a fairly standard unix-y thing, so instead of using perl, consider using the 'find' utility:

find <root dir> -atime +<days> -mtime +<days>
[download]

where <days> is the number of days in the last six months, and <root dir> is the root of the diretory tree you're searching (/ for the whole system, but it's much faster if you can just search /home for user files or something). The options I've given come from the gnu version of find, on linux. Read the man page on your local system to make sure they're correct for you.