How did Roman law get changed to allow Scipio Africanus the Younger to become consul in 147 BCE?

To become consul in 147 BCE, Scipio Africanus the Younger required an exemption from the established rules of the cursus honorum, as he was at least five years under the legal minimum age and had not served as praetor.1

When Scipio returned to Rome in 148 BCE, there was significant public dissatisfaction with the conduct of the war against Carthage, and the Roman people strongly desired to see him in command. A tribune, acting on this popular enthusiasm, threatened to veto the consular elections unless Scipio was permitted to stand as a candidate. Faced with this pressure, the Senate yielded and allowed the tribunes to introduce a bill that granted Scipio a legal exemption from the age and office requirements. This successful appeal to the popular assemblies allowed him to be elected consul and subsequently receive the African command.12