John Lennon told the rest of The Beatles that he was leaving the group in 1969. He felt that it was time for him to mature.
John Lennon met Paul McCartney and George Harrison when they were teenagers, and they performed together in The Beatles all through their 20s. When Lennon left The Beatles, he said he did it because he wanted to be able to grow up. He didn’t think it was possible to do this while in the band.
John Lennon said he felt he couldn’t mature in The Beatles
In 1969, Lennon told his bandmates that he no longer wanted to be in The Beatles. His life had been intertwined with his bandmates’ for so long and he was ready for a break.
“We’re all individuals. And in The Beatles we grew out of it,” Lennon said in The Beatles Anthology. “The bag was too small. I can’t impose far-out films or far-out music on George and Paul if they don’t want to do it. Vice versa, Paul can’t impose on me whatever he likes, especially when there’s no common goal anymore. We have to live our own lives separately.”
Source: Emma McKee/cheatsheet.com