There are a lot of myths about this subject.
Adult butterflies are much tougher and resilient than is generally supposed. In certain circumstances, a Brimstone can live for up to a year in the wild.
In captivity, with good husbandry, I have kept male and female Purple Emperors alive, healthy and well for up to eight weeks. Yes, two months.
Good husbandry means correct feeding levels, adequate activity and exercise ... 24/7 TLC.
I have found that in captivity a male Purple Emperor can be more virile and capable of better successful pairings with higher levels of fertile ova when over one month old. Males used for pairings say only six or seven days old have far lower or less successful fertility. There's a reason why males emerge a week or more before the females do. Indeed a good male can be used for several successful pairings over a period allowing time for him to recover, feed up and restore virility between pairings...
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Under very favourable circumstances and lots of luck, I suspect the same could happen in the wild.
As observed in an earlier response on this thread, during long periods of adverse weather conditions, insects can lay up switched off and so do not age at all. Just taking the occasional sip of rainwater or morning dew to sustain them. Then resume an active life when conditions and temperatures improve.