Just looked a couple up:
G-AWNA 747-136 entered service Apr'70, retired Oct'98
G-AWNF 747-136 built '70 still in service Aug '99.
So near enough 30. Lufty of course also well known for 747 preservation.
The oldest BA 777's are around 20, so plenty of years left. A few of the 76's left in service approaching mid'20's.