This isn't quite correct either, because "seniority" is not necessarily equivalent to "age". The age distribution, even in BA's seniority list, is not monotonically decreasing.
correct SR71, thats why you cannot use seniority!
Seniority is a union controlled list, it is not recognised in law. The last "merger" was Bcal and that caused all sorts of political fall out, and the only reason they got a "merger" was that they bought a significant longhaul fleet to the fold, Dan air (the few that were) cityflyer etc all were tagged on the bottom (with short haul command grandfather rights), i rather suspect that this is what will be in store for the BMI guys and girls. HOWEVER BA stated that they would not allow pilots to join BA mainline without passing the BA selection procedure, (applied to BACON and OPENSKIES pilots) so possibly another obsticle in the way. Its going to be messy whatever happens.