WannaBeAParrot, not a cherry head...
Here's a website that shows head shot comparisons between the different species of "red headed" conures - not taking subspecies into account.
Hideaway Farms Aviary
Punk, I guess another way of saying it, is if you had a child and he/she was acting odd, or not the way they should be, would you take them to a doctor to make sure everything is ok or leave them at home? Birds can't tell us when something is wrong, except when their behavior isn't quite right. It could be subtle things such as a change in weight, different droppings, slightly more sluggish behavior (could be so minute that it's hard to tell until the bird is well again). Short of finding a mobile avian vet, it's usually more beneficial to take a bird in to an a-vet and get them treated rather than leaving them at home possibly getting sicker.
I know it's a big concern about heat, cold and the stress of it... but it's really a no win situation if your bird doesn't enjoy going places. Older birds especially need to be watched over for health problems that aren't as common in the younger birds.
I don't get the vibe that he's cage territorial so much as he doesn't enjoy human interaction. If people must grab him out of the cage to remove him, or use a towel, he finds this experience scary and makes him not want to trust people. I would have to see his behavior or hear more about it.
A lot of people mistake fear as aggression. Birds have a fight or flight response. Once flight (escape) is taken out of the equation (birds are clipped then stuck inside a cage), that leaves fighting (aka defending themselves). It is very possible to teach a fearful parrot to be aggressive. In short though, a fearful parrot is one that tries to get away from you, avoiding you at all costs. A parrot that is aggressive will go out of their way to attack you. It's easier to work with a bird once you understand their behaviors better.
If the leg band is closed, that's proof that he was captive bred and may help you determine how old he is. My mitred conure is also banded. Because of his band, I was able to figure out his age (was told he was around 10 years old, but he was really 12, and now he's 18), that he is not a part of the wild flock of cherry heads in San Francisco (as some thought or fantasized about), and that both of his parents were wild caught imports.
Here's some photos of Charlie that also kind of show his leg band...
The band might be traceable.... I can try myself if I know the info on it... although that depends on whether or not there is any information left about the breeder who bred him.