Actually the Yellow collard macaw can live to about 50 years according to The World Parrot Trust.
First I want to thank you for rescueing him, secondly I would like to welcome you to the forum. Now for the part of this that I hate, I need to ask you to try to find this birds owner, the one that he escaped from. They should be looking for him and feeling really heartbroken over this. Call any avian vets office in a 50 mile radius from where you found him and do a public service announcement on local radio stations and perhaps talk to the newspapers in your area all in an attempt to find his humans. You should not mention the species of macaw that he is nor should you give out the information on the band as these can be used to identify him. If you get no answers to these attempts then he is rightfully yours to keep. Although this is the hard part it is the right thing to do and I know that if he were yours and some how had escaped into the human world that you would want whoever found him to try and find you as well. Please disregard this if you have already done these things.
I would really like to help you so I need to know what you are feeding him as he can not remain healthy on a diet of seeds or pellets alone, he is going to need to have fresh fruit and vegetables, preferably organic so as to avoid as many pesticides as possible not to mention all of the other chemicals that are put on our foods while they are growing and or processed for sale.
Here is what The World Parrot Trust has to say about this macaws diet, consider it as a starting point
Diet:
Dried figs soaked in water a few hours, two or more per bird daily, with one drop of Konakion (Roche) or other vitamin K additive, once daily; fruits forming at least 50 percent of diet; soaked sultanas; berries (elder, mountain ash, pyracantha); spray millet; small seed mix with: canary, oats, safflower; cooked pulses; rearing food with: hard-boiled egg, wholegrain bread, low-fat cheese and carrot, all ground to crumbly consistency; for breeding: live food (mealworms) if taken; commercial insectivorous food; variety of vegetables; walnuts; complete pellet.
Please make note that this bird needs to have a daily vitamin K supplement and please be aware that not all of these foods are appropriate for this bird due to his age, for instance he does not need rearing foods and mealworms would only be needed during his breeding cycle.
Parrots are photoperiodic ( research this) which means that several of their annual cycles such as molting and breeding are largely controlled by the type and amount of light that they receive daily. They can not adjust to a human light cycle so it is up to you to see that they are exposed to the twilight periods of both dawn and dusk daily to keep their internal biological clock functioning properly, these times must be without any artificial lights on to interfere with the light at these times. This means that they need to be on what is referred to as a solar light schedule just like the wild birds outside, getting up with the sun and going to sleep by the time it is dark outside as well.
Since this bird is about 14 inches long or a little loner he has a wingspan of about 28 inches and so he needs a minimum cage size of at least 30 inches and tall enough that a perch placed about 16 inches from the top will be about your eye level or close to it. This is the smallest cage size for this size of bird and is only adequate if he gets out of the cage for a minimum of four hours each and every day.
He is going to need a lot of toys, especially ones that he can chew up and destroy, blocks and sticks of untreated white pine or fir would be about the cheapest wood that is bird safe to begin with for destructible toys. If he does not know about toys then you will have to teach him.
I don't know how much you do or do not know, but you said that you are new so I have been taking this from a beginners starting point.
If you have not already discovered this the hard way, then you need to know that parrots bite, all parrots bite, mostly out of fear but also as a means of disciplining us. A bite from a bird of this size and beak strength is no laughing matter as it can cause some serious damage.

Now you know how pirates got their eye patch and holes for their ear rings

Until you get to know this bird better please don't let him on your shoulder although that is probably where he will prefer to perch when on you.
You have a lot to learn and the faster you learn the better of you and the bird will be. Here is a link regarding toxic and non toxic things that you need to know, the listing begins on the second page of the link and covers many things from foods to household items.
viewtopic.php?f=8&t=12521 This will give you a starting point, please feel free to ask any questions you may have.