There are many people, happily flying with BA, to mention but one,longhaul all over the world on their 767 and 747 fleet. Most are blissfully unaware that the aircraft is the same age, or older in some cases, as a lot of the Jet2 fleet.
They have no qualms because BA is a trusted brand and the standard of engineering is excellent. Ditto Jet2. I think people mention the age simply out of ignorance or to do them down tbh...
Last year flew on G-CELJ and G-LSAA..both venerable, but the cabins were immaculate, very comfortable, good legroom and excellent crews..I hope they prosper for many years to come..