B&G's have a tendency to have allergies to CAG dust. It would be better to keep them as far away from each other for this reason if no other.
As far as having two birds of very different sizes out of the cage at the same time, I usually don't suggest it but it is a matter of supervision, temperment, and "neutral" places.
First supervision, never let birds of large size differences out at the same time unless they can be very well supervised. Even birds that have gotten along well can become startled and take it out on the nearest object, person, or animal. That is why a tame bird at times will still bite their "most loved" person. If a macaw becomes startled and bite an african grey or amazon etc it can do a lot of damage even if that was not the intent of the bird. Most accidents can be stopped if supervised closely but there is still that potential for not being able to stop it quickly enough.
Next aggression. If one bird acts more aggressive no matter whether it is the smaller or larger birds there is a big potential for problems. If one bird wants to guard its space from the other a fight can ensue leaving more than likely the smaller bird injured. "Usually" CAGs are not aggressive and instead are more timid so it would probably avoid conflict but if it felt threatened by the macaw it might bite and show aggressive behavior. As far as the macaw they can be quite friendly birds but if startled one hard bite could be enough to kill or seriously injure the CAG.
"Neutral" places. Since your CAG has been there longer it is going to see much of the house, playgym, stand etc as its property. Because of this it may feel the need to guard its territory against the larger bird causing conflict. Also if there is one place the macaw likes to play it may fight if the CAG comes near that spot.
I know some people can have all different sizes of birds out at the same time and we do in fact have several birds out at once but we try to have at least two supervising people if not more (depending on the number of birds out) to keep a close eye on them. We also have certain "playstations" set up for each different bird or type of bird. Now sometimes one will decide to go visit another playstation and if not watched carefully that could cause a problem. We have luckily never had a problem with this yet but we have seen where it could have happened if we hadn't been right there!!