Paul made the bizarre admission in a recent GQ magazine interview, in which he described how as youngsters he, John and other pals had masturbated together in a darkened room at the "Imagine" singer's childhood home.
Asked about the incident by TMZ, Ringo, 78, explained that the incident occurred before he knew his bandmates, saying: "Well that was before I joined."
He and his wife Barbara Bach, 71, then laughed after being questioned as to whether he felt he'd missed out by not being present.
Although John and Paul were childhood friends, and George Harrison joined them in their early band The Quarrymen in 1958 aged 15, Ringo, real name Richard Starkey, only met his future bandmates in Hamburg, Germany in 1960, and became a member two years later when he replaced fired drummer Pete Best.
Describing the youthful indiscretion in the GQ chat, Paul said, "Instead of just getting roaring drunk and partying... I don't even know if we were staying over or anything... we were all just in these chairs, and the lights were out, and somebody started masturbating, so we all did."
He went on to reveal how the group of friends had then encouraged each other to shout out the names of the pin-ups of the day, like Brigitte Bardot, and described the group masturbatory session as, "harmless fun."