Do this to use my idea:

...

# add this line
my $maxval = 0;
foreach (@array) {
    $maxval = $_ if $_ > $maxval; # and populate as needed here
    print $_, "\t";
    $counter ++;
    if ($counter % 4 == 0) {
        print "\n";
    }
}

# then include the value in your final print statement
print "The largest element is: $maxval\n";
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On the other hand, to use max as shown by Rolf do this:

use strict;
use List::Utils qw/max/; # add this line

... # rest of your code is unchanged

# and then use the function in your final print statement
print "The largest element is: " . max(@array) ."\n";
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