In my flock, oldest bird by species average lifespan would be my bourke parakeet. Their expected lifespan is 11-15 years. My hen is 17-19 years old. I've only heard of two older than her and I think one is still alive!
My mitred conure is 20 this year.
I have a cockatiel that I know he is *at least* 16 years old, but he could very well be in his twenties or older. I have two other tiels of ages unknown, but I'm assuming they are also older birds.
One of the local bird club members owns a B&G that's 40 years old.
I did meet a DYH zon that had gone through three generations of one family and when I met him he was in his 50's. If he's still alive (I hope the cage he was in is not his permanent residence! At best, it's only large enough to open one of his wings and fits on top of a counter!) then he might be in his 60's by now.
My avian vet said that she got to see/meet a B&G that was 104(?) years old!
I know someone who had a male canary die short of his 20th birthday. As I understand it, the average canary life is usually 3-6 years. 12 years in age is pretty good for a canary!
Cockatiels probably live about 8-15 years on the low end, and 18-25 on the high end. I've come across quite a few owners who had cockatiels die or still living at the age of 35!!!
There is a quaker that *possibly* lived into his 50's, assuming the information on his leg band was correct.
There are conures who are 40+ years old (and someone recently mentioned another conure in his 50's).
So assuming that the birds can remain relatively healthy, if not in great health, and barring accidents, they can have extremely long lives!