use Data::Dumper;

my @array  = (
    ['ashok',15,'2006-01-01'],
    ['ashokpj',15,'2006-02-01'],
    ['ravi',56,'2006-03-01'],
    ['raja',56,'2006-02-01'],
);

my @res = do {
    my %group;

    for (@array) {
      # $group{$_->[1]} = $_ if $_->[2] gt $group{$_->[1]}; bad
        $group{$_->[1]} = $_ if $_->[2] gt $group{$_->[1]}[2];
    }

    sort {$a->[1] <=> $b->[1]} values %group;
};

print Dumper \@res;

__END__
$VAR1 = [
          [
            'ashokpj',
            15,
            '2006-02-01'
          ],
          [
            'ravi',
            56,
            '2006-03-01'
          ]
        ];