Biden, once one of the nation’s youngest senators, will be its oldest president Michael Rosenwald Joe Biden, right, was once one of the youngest senators. Now, he s about to become the nation’s oldest president at 78. (Bettmann Archive/Getty Images) In December 1972, not long after winning a U.S. Senate seat from one of Delaware’s oldest political hands, Joe Biden began traveling to Washington to introduce himself around town. Strapping and handsome, Biden had just turned 30, the minimum age to become a senator. Now, almost 50 years later, he is about to become the nation’s oldest president at 78. Back then, he was the sixth-youngest senator in U.S. history, according to the Senate website.