July 6, I missed a day.

From MSNBC Entertainment
Paul McCartney and John Lennon met for the first time on July 6,
1957, at the St. Peter Church Fete in Woolton, Liverpool, England.

Prunie Ed: John was 17 and Paul was 16

Lennon was playing in his band, the Quarry Men, and a mutual
friend and sometimes band mate, Ivan Vaughan, brought
McCartney along and introduced the two.