After months of holding off, Democratic presidential rivals are now taking jabs at what many campaign operatives view as front-runner Joe Biden’s biggest vulnerability: his age.

A prominent South Carolina Democrat who is a supporter of California Sen. Kamala Harris has been the most direct in attacking the 76-year-old former vice president, who was first elected to public office in 1970. “Joe Biden has been running for president since before I was born,” former state senator Bakari Sellers said this week.