my $confpath;
my $servername;
my $filepath;
my $filemaxage;

$confpath = "/export/mksysb";
$filepath = "/export/mksysb";
$filemaxage = "360";
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The usual practice is to define and initialize variables in the same step:

my $confpath   = '/export/mksysb';
my $filepath   = '/export/mksysb';
my $filemaxage = 360;
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By the way, $confpath and $filepath have the same value so is there really a need for two variables?

while(<FILE>){
    chomp($servername = $_);
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That is usually written as:

while ( my $servername = <FILE> ) {
    chomp $servername;
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        if (-M $_ > "$filemaxage"){
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You are converting $filemaxage to a string and then Perl has to convert it back to a number in order to do a numerical comparison.

What's wrong with always quoting "$vars"?

        mkdir("$filepath/$servername");

system("nim -o define -t mksysb -a server=master -a mk_image=yes -a lo
+cation=$filepath/$servername/$servername\_`date +%m%d%Y` -a source=$s
+ervername $servername\_`date +%m%d%Y`");
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You should also check for failure with mkdir and system like you already do with open and unlink.