The way these numbers are calculated are often problematic.
As a bird researcher (songbirds, not parrots), people often ask about lifespans of sparrows - but the lifespan of birds is so different from humans or even most mammals that it's hard to make meaningful comparisons.
If anyone likes numbers, we humans tend to follow a normal distribution in our lifespan (ok not quite, but close enough). This means there is a roughly bell curve distrubution of ages to which people live. The mathmatical average is the same as the most common. I don't know human life spans, but lets say it's 80. The average life span is 80, and most people live to be about 80.
But now lets look at sparrows. They don't have a bell curve distrubution - they have an exponential decay. Of 1000 hatched only a very small percentage of those may survive to be a year old, then a fair portion of those that remain will live to be two, and some percent of those will live to be 3, etc. The "average" lifespan is thus greatly influenced by the massive number of individuals that don't even survive their first year. So the "average" may be 6 to 7 months perhaps. But it is not terribly uncommon for a house sparrow to live 8-9 years. The oldest on record was 13 years old. So how do I answer when someone asks how long does a house sparrow live? The answer: it depends. They don't die of "old age" as we do. They die from accidents, predators, etc.
Much of this also applies to parrots. Senesence (old age) isn't as big of an influence on parrot life spans as it is for humans (and most mammals). So a well cared for parrot who doesn't get any diseases or other health problems can live a very long time. Unfortunately there are *a lot* of ill-educated parrot owners who's parrots die very young from cooking fumes, accidental escapes, infections from interacting with another pet, etc.
So how long CAN a conure live, and how long DOES a conure live are entirely different questions.
EDIT: a big part of this is many of the things we are used to dealing with do follow normal (aka bell curve) distributions. With normal distributions, the mean, median, and mode of the numbers will be very similar. Each of these (mean meadian and mode) could colloqiually be thought of as an "average" or "estimate", for normal distributions you can use them interchangeably and get roughly the same answers. For exponential decay, however, the mean median and mode can be drastically different. Or in less numerical terms: no matter what method of estimating a human lifespan we use, we'll get similar numbers; but for each method of estimating avian lifespans, we can get drastically different numbers. So when a source says conures can live to be 20-30 years, or 5-7 years, or whatever, it is important to know what those numbers actually represent.