If you're sorting $a cmp $b the most recent will be in the last element rather than the first so pull out $sorted[-1] instead. The alternative is to swap the order of comparison ($b cmp $a) and then the most recent will be first.

#!/usr/bin/env perl
use 5.032;

my @dates = qw( 02-03-2003 03-01-2015 01-15-2022 );
my @sorted = sort { my $new_a = join( q{-}, (split(/-/,$a))[2,0,1] );
                    my $new_b = join( q{-}, (split(/-/,$b))[2,0,1] );
                    $new_b cmp $new_a } @dates;
say $sorted[0];

__END__
$ perl blonk.plx
01-15-2022
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