As has been pointed out, the Beatles started breaking up at the "dangerous" age of 28 - many people have changes of direction in life at around 28.

Lennon was 28 in 1968 when work on the White album started arguments in the band, Ringo - also 28 in 1968 - walked out of the band, but was persuaded to return. By the time Let It Be was being made in 1969, George (who was then 26) also walked out but persuaded back to make one good album - Abbey Road.

At the end of Abbey Road, when the Beatles effectively stopped working together, Lennon and Starr were 29, Paul was 27 and George was 26.