I agree with April. While genetics and temperament play a big role, I still believe that almost every EM will show guarding ability to some extent. Bane is now 14 months, and we have started seeing it in him. He‘s totally gentle, calm, and great with people, but whenever an unfamiliar person accesses the house (e.g. technician), you can tell that he first goes into protection mode. He would never do anything, but you can tell that he is alert, and his bark is very intimidating (he rarely barks at all). Many people say that the true nature often does not show until 2-3 years of age.
Regardless, Gus looks great. As stated before, he definitely is going to be big.