Elizabeth and Philip were first introduced to one another when the former was just eight years old, at the wedding of Princess Marina of Greece and Denmark (Philip’s cousin) and Prince George, Duke of Kent (Elizabeth’s uncle) in 1934. Five years later, when Elizabeth was 13 and Philip was 18, they met again at the Royal Naval College in Dartmouth. It was here, reportedly, that Elizabeth fell in love with her future husband, and they later began exchanging letters.
In 1946, Philip asked King George VI for his daughter’s hand in marriage. The king agreed on one condition – that the formal announcement of the engagement was delayed until Elizabeth turned 21 the following April. According to reports, both the king and his wife Queen Elizabeth were reluctant to approve the marriage out of fear that their daughter was “too young”.
https://www.historyextra.com/period/20th-century/queen-elizabeth-prince-philip-milestones-marriage-relationship/