My biggest question is, how do you know how old he is...was it a single owner who gave him up and knows where he came from? Possibly two owners...passed down through a family member? I really have a hard time believing claims like that because so many people don't know for sure, especially if the bird has been passed from one person to the next. Also, if this bird can truly be traced all the way back to 40 years ago, that would be 1971 and I'm sure he would have most likely been a wild caught bird rather than domestically bred. In that case, there's no way to know how old he is because they most likely didn't know his age when he was removed from the wild.
I will say that Cookie, MM2 at the Brookfield zoo in Chicago, is at least 78, because they've had him that long. MM2s are generally about the size of a Goffin's, maybe a bit bigger. Severes are bigger than that. I would think that the bigger the bird, the longer it lives but that's just a guess and will definitely depend on diet and exercise throughout its lifetime.