Right now he is not only going through his first big molt, which is the largest molt he'll ever go through, but he's also probably starting to go through puberty, which is the longest and most difficult hormonal phase that he'll ever go through. So that is probably what is playing the largest part in his sudden aggression. All parrots typically become at least a little aggressive, grumpy, cranky, etc. while going through puberty, but IRN's seem to be one of the species that takes it the hardest. And while I know this is frustrating, you do need to have patience with him, because this isn't his fault, and punishing a bird doesn't work anyway, they don't respond to punishment or negative-reinforcement, but when it's due to puberty and isn't his fault, then the punishing him or yelling/scolding him isn't going to help the situation. So try to be patient with him while he goes through this...
At the same time, you can't have him flying at your faces and biting people. Cage-territoriality is completely normal, some parrots species are worse than other with that, Quaker Parrots and IRN's do tend to be some of the worst when it comes to being extremely territorial about their cages, so as far as that goes it's best to simply open his cage door up and let him come out on his own, don't reach in to get him out, and try to respect his "territory", it's his "safe-space", so using it as a punishment typically doesn't work either.
He is definitely testing his boundaries as Triggs mentioned above, and you need to make sure that you're not letting him get what he wants when he does these things, otherwise he's going to simply continue to do them because he knows he'll get what he wants. You should try the "Shunning Method" whenever he bites anyone, and see if he responds to that...Basically this means that whenever he bites anyone, you immediately tell him "No Bite!", do not yell at him but simply say it to him each time immediately when he bites, and then immediately put him right down on the floor and everyone in the room must then turn your backs to him. Literally, you turn your backs to him. And you must then completely ignore him for 5 minutes. Any shorter and it won't do any good, any longer and he'll lose interest. All parrots HATE being on the floor, because they are the lowest thing in the room, and it takes away all feelings of dominance that they have. During the 5-minute "Shunning" period, you cannot look at him or make eye-contact with him, you cannot say a word to him or acknowledge him when he makes a noise. You simply all stand there with your backs to him while he's on the floor...If he walks around in front of you to face you, you simply keep turning your back to him. If he climbs up your leg or flies to your shoulder, you simply put him right back down on the floor without saying anything. If he flies over to his cage top, I usually just leave them there but keep my back to them and keep ignoring them for the 5 minutes. And when the 5 minutes is up you don't automatically go back to talking to him or acknowledging him, you just walk away or go and sit down and pretend like nothing happened...And if he immediately bites you again, then you have to immediately say "No Bites!", put him down on the floor, and turn your backs to him again for another 5 minutes, and do this as many times as you need to until he gets the point.
I've seen this stop a parrot from biting in literally one day. That first day you'll probably end-up doing the Shunning-Method a bunch of times, sometimes a bunch of times in a row, but that's what it takes for them to get the point. Once they understand that they aren't going to get what they want and biting isn't going to help him get it either, and they understand that ANY TIME THEY BITE they are going to be totally ignored and put on the floor, they do usually stop directly. And any time he "wants something" like to chew on something he should't, you need to do the same thing, take whatever it is away from him immediately and tell him "No Chewing!" (a different Verbal-Cue for each different behavior, as parrots understand the difference), and you certainly cannot "use a treat or his favorite treat to distract him when he's biting or chewing on something he shouldn't be", by doing that you've accidentally/inadvertently encouraged him to do the bad behavior. You simply have to take the keyboard or whatever it is away from him and tell him no, and walk away from him.
If the flying at you and biting you continues, the next step that I personally would take would be to clip his wings, as this is a situation where it's dangerous to people in the house, and it's dangerous to him as well. And when you clip their wings they tend to lose a lot of their feeling of dominance as well...And if you do have his wings clipped, and it's done correctly, they will fully grow back-in in about 2 months or so, so you need to take full advantage of the time his wings are clipped to work with him on his bad behaviors, so that by the time his wings grow back in he'll not just go right back to doing the same things. You should always have their wings clipped by an Avian Vet or a breeder who knows what they are doing, and you need to ALWAYS REQUEST OR DEMAND that they only clip the outermost 5-6 Primary Flight-Feathers on EACH WING. This will ensure that they will grow back fully in about 2 months or so...It's temporary, it's painless, and if you take full-advantage of the 2 months you have where he can't fly, when his wings do grow back he should be trained and the unwanted behaviors should stop. There will be people who say not to clip their wings, it's a personal choice that each individual bird owner needs to make for themselves, it doesn't hurt them at all, and it's very temporary...In a situation where a bird is flying at faces and biting people, it's a safety situation for you and the bird, so I personally feel that it's perfectly fine to clip their wings, as long as you train the bird/work with the bird during that period and you then allow his wings to grow back in again.
