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
Of the men, who were neither unconditional adherents nor open opponents of the Sullan constitution, no one attracted more the eyes of the multitude than the young Gnaeus Pompeius, who was at the time of Sulla's death twenty-eight years of age (born 29th September 648). The fact was a misfortune for the admired as well as for the admirers; but it was natural. Sound in body and mind, a capable athlete, who even when a superior officer vied with his soldiers in leaping, running, and lifting, a vigorous and skilled rider and fencer, a bold leader of volunteer bands, the youth had become Imperator and triumphator at an age which excluded him from every magistracy and from the senate, and had acquired the first place next to Sulla in public opinion; nay, had obtained from the indulgent regent himself--half in recognition, half in irony-- the surname of the Great.
Unhappily, his mental endowments by no means corresponded with these unprecedented successes. He was neither a bad nor an incapable man, but a man thoroughly ordinary, created by nature to be a good sergeant, called by circumstances to be a general and a statesman. An intelligent, brave and experienced, thoroughly excellent soldier, he was still, even in his military capacity, without trace of any higher gifts. It was characteristic of him as a general, as well as in other respects, to set to work with a caution bordering on timidity, and, if possible, to give the decisive blow only when he had established an immense superiority over his opponent. His culture was the average culture of the time; although entirely a soldier, he did not neglect, when he went to Rhodes, dutifully to admire, and to make presents to, the rhetoricians there.
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Reference address : https://www.ellopos.net/elpenor/rome/5-01-lepidus-sertorius.asp?pg=12