Who is the youngest actress or actor?

As of my last update in September 2021, the youngest actor to have ever performed in a Hollywood film is Brandon Quintin Adams. He was just six months old when he starred in the 1996 film "Sgt. Bilko."

However, it's worth noting that the entertainment industry is constantly evolving, and there may have been younger performers who have emerged since then. To stay up-to-date on the latest information, I recommend checking reputable sources like Guinness World Records or IMDb for the most current records.