Everyone can be creative, but can everyone be a creative director in advertising?

It depends on exposure of the creative one. how the creative one be motivate, dedicated and inspired to his or her work.. for me ... Yes every details of job, exposure and knowledge is enough to become a creative director because most of the creative person is competitive...

being a creative director is based on three things: 

creative thinking

leading skills

and team work :)

so not everyone can do it 

Absolutely not. People often mix up the creative side with the creative management  and it never work as people act as creative not as creative director meaning in charge of a creative dpt with all the responsabilities that goes with it. I have had so many time the mandate to regenerate creative dpt because of agency making this basic mistake and ending with the "CD" being fired by client or good creative leaving for competition with the result of a drop in the creative quality. 

of course not .we sometimes say that the director is wonderful in designing the advertisement specially when we see something that isn't usual and sometimes something that is very realistic or funny.

Only he or she uses the standards they have acquired over their years in the business to say what is good, and what is bad. They direct the work to make the good work better, to make the creative briefs say just what they should be saying, and to make the bad work disappear.