Luden you have to remember that peasants, that's the low classes, were starving to death. As for quality, our food certainly isn't rotting or rotten, and we make sure they are properly cooked, stored, preserved (think about it, a Roman Emperor possibily died of food poisoning, what would food be for the average joe?). And we get all kinds of vegetables and fruits and meat all year round while they are restricted by when those vegetables actually ripen (and the average joe won't be getting much meat at all).
apple that life expectancy (you altered the quote

, though I admit it was badly worded

) is the average of a society using demographic model West level 3 (the model that researchers say fits for the Romans) for females. So you have to add like 5 to 7 years for elites and then take away like 2 for average between sexes (females tend to live longer).
Here's the list of Roman Emperors that were not assassinated or killed in some way. Info's off wiki, with name, age at death, and cause of death when available. Remember this is not just a "rich Roman" but the EXTREME TOP of the society. So you have to decide for yourself how many years to take away for a general "rich Roman". On top of that, this is also sort of life expectancy of people who survived long enough to actually become emperor... (so I say take a few more years for a general class of society)
Augustus - Age 75
Tiberus - Age 77 (possibily assassinated)
Claudius - Age 63 (possibly assassinated)
Vespesian - Age 69 Intestinal inflammation which led to excessive diarrhea
Titus - Age 41 Illness
Nerva - Age 67 Stroke
Trajan - Age 63 Edema
Hadrian - Age 62 Heart Disease?
Antoninus Pius - Age 74
Lucius Verus - Age 39 Food poisoning/plague/smallpox
Marcus Aurelius - Age 58
Septimius Severus - Age 65 Illness
Gordian III - Age 19 (possibly unnatural causes)
Hostilian - Age 21~ Plague (possibily smallpox)
Valerian - Age 60 (died while in captivity)
Claudius Gothicus - Age 56 Plague (possibily smallpox)
Marcus Claudius Tacitus - Age 76 (possibly assassinated)
Carus - Age 56 death by lightning?

Diocletian - Age 66
Constantius Chlorus - Age 56
Galerius - Age 51 Disease
Constantine I - Age 65 Illness
Constantius II - Age 44 Illness
Jovian – Age 32 (Carbon monoxide poisoning)
Valentinian I - Age 54 Burst blood vessel in the skull while angrily yelling at people
Theodosius I - Age 48 due to Edema
Arcadius - Age 31
Honorius - Age 38 Edema
Theodosius II - Age 49 Riding accident
Constantius III - unknown (birthdate not known)
Marcian - Age 60 Disease (possibily gangrene)
Olybrius - Age 41 Edema
Romulus Augustus - unknown (birthdate not known)
Leo I - Age 73 Dysentery
Zeno - Age 66
Anastasius I - Age 88
Justin I - Age 77
Justinian I - Age 81 (got the plague but survived)
Justin II - Age 58
Total: 39 (unknown age 2, known 37)
Cause of Death
Disease excluding edema and “falling ill” after age 60: 9 or 10 (23~25.6%)
Edema: 4 (10.2%)
Not listed: 10 (25%)
Average life span out of 37 = 57.2 years
Standard Deviation = 16.3
Average life span excluding longest surviving 4 and shortest surviving 4 = 58.4 years
Having 1/4 to 1/3 of natural deaths resulting from some form of disease sounds about right for pre-modern times (did someone say they had great medicine and health care systems back then?).
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