Quentin

masc. proper name, from Latin, from Octavius, from octavus "eighth," from octo (see eight).

But although we find so marked differences in the use of the numerals as names, it is impossible to believe that this use did not arise in the same way for all; that is, that they were at first used to distinguish children by the order of birth. But when we find them as praenomina in historical times it is evident that they no longer referred to order of birth. [George Davis Chase, "The Origin of Roman Praenomina," in Harvard Studies in Classical Philology, 1897]