Just to satisfy my curiosity, I tested your code against 5.8.8 and 5.10.1 using the re pragma. Under 5.8.8, it doesn't work; however, under 5.10.1, it works. Evidently, the regex engine has improved immensely. Try this and see what the result is:

#!/usr/bin/perl

use strict;
use warnings;
use re qw(debugcolor);

my $names = 'Fred Flintstone and Wilma Flintstone';

if ($names =~ m/(?<last_name>\w+) and \w+ \g{last_name}/) {
    print "I saw $+{last_name}\n";
}
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