Caesar didn't pick the month of Quintilis to be named after him, it was renamed the Julius after his death by a consular law proposed by Antony in 44 and passed by the assembly. Macrobius tells us that Antony chose the month of Quintilis because Caesar was born in that month on the fourth day before the Ides, i.e. the 12th. Cassius Dio thinks that the change in name of the month of Quintilis was due to a law passed by the Triumvirs, but the sources seem not to support him in this.