Julian Lennon was 21 years old in 1984, since he was born on April 8, 1963.

Quick math

  • Born: April 8, 1963
  • In 1984, he turned 21 on April 8
  • So he was 20 before April 8, 1984, and 21 for the rest of that year

Tiny context

That lines up with reports from 1984 noting he was 21 at the time.