Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Custom, indeed, had long prescribed both of these; but it was a sensibly felt restriction of the freedom of election, when the customary qualification was raised into a legal requirement, and the right of disregarding such requirements in extraordinary cases was withdrawn from the elective body.
In general, admission to the senate was thrown open to persons belonging to the ruling families without distinction as to ability, while not only were the poorer and humbler ranks of the population utterly precluded from access to the offices of government, but all Roman burgesses not belonging to the hereditary aristocracy were practically excluded, not indeed exactly from the senate, but from the two highest magistracies, the consulship and the censorship. After Manius Curius and Gaius Fabricius,(16) no instance can be pointed out of a consul who did not belong to the social aristocracy, and probably no instance of the kind occurred at all.
16. Cf. II. III. New Opposition
But the number of the -gentes-, which appear for the first time in the lists of consuls and censors in the half-century from the beginning of the war with Hannibal to the close of that with Perseus, is extremely limited; and by far the most of these, such as the Flaminii, Terentii, Porcii, Acilii, and Laelii, may be referred to elections by the opposition, or are traceable to special aristocratic connections.
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Reference address : https://www.ellopos.net/elpenor/rome/3-11-government-governed.asp?pg=17