"The higher pay that many senior engineers command is the cause."
If higher pay is what it's all about, Meggot and Minions should have been way-long gone!
There's another solution at hand, and Meggot and Minions (and other large corporations) just cannot see it... As people get older and money gets tighter and older folks slow down... The plain fact is, lots of older folks do slow down... Cut their pay! Duh!
For those who get all miffed about their cut in pay, document their trouble-making, and fire them! For those who are happy to keep their jobs at lower pay... There WOULD be many of these... Keep them! That's a win-win!
But Meggot and Minions would rather use blatant age discrimination and pay the legal costs as a regular "cost of business". Besides, it makes them feel WAAAY superior and smug, to be old but overpaid slowing-down geezers, firing other (lower-paid) slowing-down geezers who are inferior to their smugly superior selves... Do NOT underestimate the power of smugness!