Per the OP (for easy ref since we're this far down the thread):

if (time - $ftp->mdtm($_) > $maxage) { push(@return, $_); }

I have looked at the code and it didn't helped. So I tried to find what is unitilized but I haven't found anything:

• time: function
• $ftp->mdtm($_): function,...

Are you quite sure that "time" -- which looks (to me, YMMV) a lot like a bareword -- is a function rather than a typo for time() or something similar?