He’s been known for making gaffes since he was Obama’s vice president. From his Wikipedia page:

The remark revived Biden’s reputation for gaffes.[227][221][228]

Those sources are from 2009.

Journalist and TV anchor Wolf Blitzer has called Biden loquacious;[692] journalist Mark Bowden has said that he is famous for “talking too much”, leaning in close “like an old pal with something urgent to tell you”.[298] He often deviates from prepared remarks[693] and sometimes “puts his foot in his mouth”.[169][694][695] Biden has a reputation for being prone to gaffes[696] and in 2018 called himself “a gaffe machine”.[697][698] The New York Times wrote that Biden’s “weak filters make him capable of blurting out pretty much anything.”[169]

He has struggled with a stutter most of his life, which he learned to cover up.