The length of your account password has nothing to do with you be able to access your saved passwords or not.
Like I said, Opera encrypts your saved passwords locally using your OS password and on sync using your Opera password. So if you forget your account password, you can't get your saved passwords from sync.
The minimum length of 12 characters is to increase the security of the user data. All serious sites nowadays ask for at least a 8 character password and sooner or later that number will increase to provide more security.
Most specialists recommend that you use a password as long as possible, with numbers, letters and special characters in it.