# get a list of data files that are at least one day old in /my/tmpdir:

opendir( TMP, "/my/tmpdir" );
my @dayold = grep { /[^.]/ and -f and -M _ > 1 } readdir TMP;

closedir TMP;

# don't like old files?  kill 'em off:
unlink map { "/my/tmpdir/$_" } @dayold;