In Mommsen's History of Rome from the 1850s he argues that although the year of Caesar's birth is usually given as 100 B.C. because Suetonius, Plutarch, and Appian all state that he was in his fifty-sixth year at his death, there are reasons to doubt that:
But this account would make him enter upon the three offices of aedile, praetor, and consul, which he held in 65, 62, and 59 B.C. respectively, in his thirty-fifth, fortieth, and forty-third years, that is, in each case, two years before the legal time. The fact that this irregularity is nowhere noticed, suggests that the statements of Suetonius, Plutarch, and Appian are errors derived from a common source, especially as such errors must have been common before the commencement of the acta diurna. The date 102 B.C. would agree better than 100 B.C. with the statement of Velleius, that Caesar was appointed Flamen Dialis when paene puer; since the latter date would make him thirteen years six months old, i.e., not almost, but actually a boy. Further, the number LII on the coins struck by Caesar about the outbreak of the civil war would agree with the years of his life if he was born in 102 B.C.
Today his birth year is still given as 100 B.C. in reference works, although Wikipedia has a note which makes it sound like the argument isn't quite over yet: "There is some dispute over the year of Caesar's birth. Some scholars have made a case for 101 or 102 BC as the year of his birth, based on the dates that he held certain magistracies, but scholarly consensus favors 100 BC."
I wonder if the reasons for the current consensus are essentially the same as they were for the same consensus in Mommsen's time (and his arguments just haven't been seen as very convincing). Or is there an even stronger case now with new knowledge or new arguments that invalidate some of Mommsen's reasoning?