sub is_valid {
    my $test = shift;
    return $test =~ /\Aaaa_\w{1,24}(?<=\D)\d{4}\z/;
}

##</code><code>##

for my $str (qw(aaa_gjh1_dfgdf_0009 aaa_gjh_0000 aaa_fdsfs_000 aaa_sdf_jdsh_01111)) {
    print (is_valid($str) ? "ok $str\n" : "not ok $str\n");
}