The 69-year-old told Mojo that he parted ways with the manager after the suggestion, and insisted that he still enjoys making and performing music.
McCartney said: "One of my old guys who I used to have as my manager, I was knocking 50 and he said 'I think it's time you retired'. I thought, I know what you mean, but I don't really feel like it, you know.
"And if I'm really enjoying this, why retire? So I decided against it, and got rid of him. I wonder what he thinks today. Perhaps that he was right, but hopefully not."
McCartney has released six studio albums since turning 50, including Flaming Pie, Chaos and Creation in the Backyard and 2007's Memory Almost Full.
The former Beatle is also planning to release an album of pop standards, a project he has wanted to complete "for years".
McCartney also spoke of his admiration for Damon Albarn's Gorillaz, and claimed that he would like to record a collaboration in the future.
Listen to Paul McCartney's 'Every Night' below: