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
The formation of Latin oratory took place in a similar way. The Roman youth of rank, who were even at an early age incited to come forward in public with panegyrics and forensic speeches, can never have lacked exercises in oratory; but it was only at this epoch, and in consequence of the new exclusive culture, that there arose a rhetoric properly so called. Marcus Lepidus Porcina (consul in 617) is mentioned as the first Roman advocate who technically handled the language and subject-matter; the two famous advocates of the Marian age, the masculine and vigorous Marcus Antonius (611- 667) and the polished and chaste orator Lucius Crassus (614-663) were already complete rhetoricians. The exercises of the young men in speaking increased naturally in extent and importance, but still remained, just like the exercises in Latin literature, essentially limited to the personal attendance of the beginner on the master of the art so as to be trained by his example and his instructions.
Formal instruction both in Latin literature and in Latin rhetoric was given first about 650 by Lucius Aelius Praeconinus of Lanuvium, called the "penman" (-Stilo-), a distinguished Roman knight of strict conservative views, who read Plautus and similar works with a select circle of younger men--including Varro and Cicero--and sometimes also went over outlines of speeches with the authors, or put similar outlines into the hands of his friends. This was instruction, but Stilo was not a professional schoolmaster; he taught literature and rhetoric, just as jurisprudence was taught at Rome, in the character of a senior friend of aspiring young men, not of a man hired and holding himself at every one's command.
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Reference address : https://www.ellopos.net/elpenor/rome/4-12-nationality-religion-education.asp?pg=39