You mentioned that you had just got the female a few days ago. Has she been through quarantine? Ideally, introductions should wait until the quarantine period is over, so you don't risk exposing your current bird to diseases, if it turns out she is ill. After quarantine, the birds can be slowly introduced, preferably on neutral territory. Keep in mind, just because they are male/female doesn't mean they will like each other or form a strong bond. Only time and patience will determine if their personalities are compatible. Incompatibility is a fairly common issue when breeding large parrots, since they will not necessarily accept the first bird to come along and may not breed if their selected mate is not to their liking.
Next, before considering them for breeding, I would recommend getting both birds checked by an avian vet to make sure they are in good health and rule out any issues that might complicate breeding. At six years old, your birds are still young, but old enough to breed. However, egg-laying and raising young puts a lot of stress on the parents, so you want to make sure they are in peak health and getting the best possible nutrition during the entire process.
Assuming they both pass the vet-check with a clean bill of health, next step would be to double-check that their diet and exercise levels are good. Calcium and vitamin D are especially important for the female bird. What do you feed your birds? Pellets, fresh food, nuts? Have you looked into how their diet should change while they are preparing to breed or feeding young? Do you have the necessary supplies and experience to hand-feed if necessary? Macaws are not easy to breed. Do as much research as you can BEFORE something goes wrong and gather all the necessary supplies so you are prepared for the worst.
Regarding the aviary, for macaws, especially breeding birds, bigger is better. The dimensions you listed honestly sound pretty small to me. Twelve feet in length would allow flight, but it isn't really enough space for them to escape each other, especially if you keep the airspace clear for flight exercise. In fact with a six foot depth, it is going to be pretty tight in there, after accounting for perches, feeding stations, and macaw-sized toys. Being the second largest parrot species, green-winged macaws can have a 3 to 4 foot wingspan at adulthood. A six foot depth dosn't give much room to maneuver while in flight or any space to hang anything from the ceiling without it getting in the way. And if the aviary is only 7ft high, the macaws will be flying through the same space occupied by any visitor when they stand inside the aviary, which could create additional problems. If possible, I would recommend a space that is longer, wider, and taller, like 10ft by 20ft with a 10ft ceiling.
Will you be building your own aviary or buying a pre-built aviary? How much room do you have to work with? What is your climate like? There are many considerations when constructing an aviary - be sure to research appropriate materials for parrots. Large parrots can easily destroy wood and standard wire mesh. You will need to get materials that are safe for the birds and safe FROM the birds, as well as designing the space to be comfortable and safe to inhabit. Provide shelter against cold/hot weather, predator-proofing, and safe access (double-entry) to the aviary, among other things. For breeding, you would also need to offer deep nesting boxes of a suitable size and depth. Planning an aviary is a complex project. I've only really touched the surface. Good luck on your project!
Regarding keeping your parrots tame while breeding in an aviary, I would caution that it is very likely that your birds are not going to WANT close handling or outside interference during the breeding season. Territorial aggression, nest-guarding, and "unpredictabality" is common with hormonal birds. It is not realistic to expect that your birds will be "super tame" while you are attempting to breed them, because their instincts will be telling them that you are a potential threat.
This does not mean you can't continue to interact with them and maintain a good relationship ... but you will need to be very responsive to their body language, especially when you are near the nest or directly interacting with either bird. If you are not careful, you will be bitten. If you are careful, you probably will still be bitten. Be very very careful and remain hands-off, when necessary. When breeding season is over, things should calm down. However, you may find that your bonded macaw pair prefers each others company to yours. The flock dynamic is different with two birds and one human. They will still be tame, but they may not be as interested in you and may not tolerate the same level of interaction. Take it slow and adjust your behavior accordingly.
