So I think for lack of birth certificates I can imagine the underlying process of unregistered people not being aware about their true age.
The claim that high poverty and crime rates produce such fraud feels prejudiced. also why would Sardinia be different in that regard compared to Sicily or poor regions on the Italian mainland?
Also I would be interested in how many hypothesis these researches tested on the data set and on whether they performed proper adjustments of thresholds (bonferroni correction)
I disagree. And note the claim was about "relative poverty and short lifespan".
Seems very straightforward reasoning that those in relative poverty with shorter lifespans have much more incentive to falsify their age to be older than they actually are.