Ageism
Alpine,
Seniority starts when one is first employed. Thereafter, it increases with age. "Service" is an irrelevancy - seniority is based on age from th date that one joins.
Thus, it is ageism. It is probably unlawful
This has not been tested in the courts, yet. I hope that it will be tested very soon. It impacts rather a lot of things in BA...............
BA are also running the risk of having young, low paid crew in mixed fleet, and old, very highly paid crew on old contracts.
That is ageism. Not yet tested in the courts.