First off, testing the socket connection to smtp.gmail.com:465 works great using IO::Socket::SSL:

use IO::Socket::SSL;

my $client = IO::Socket::SSL->new("smtp.gmail.com:465");

if ($client) {
  print $client "GET / HTTP/1.0\r\n\r\n";
  print <$client>;
  close $client;
} else {
  warn "I encountered a problem: ",
    IO::Socket::SSL::errstr();
}
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Result:

220 mx.gmail.com ESMTP c18sm62410hub

Then a really simple test with Net::SMTP::SSL yields a bad result:

use Net::SMTP::SSL;
use Data::Dumper;
my $smtps = Net::SMTP::SSL->new("smtp.gmail.com", Port => 465);
print Dumper($smtps);
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Result:

$VAR1 = undef;

What puzzles me is that these are very established modules. I'll report more here when I know more.