Welcome to the World of the Past!
If you look into it I think you will find that the major airlines in the States are taken to be a critical transportation resource whose disruption would seriously impact the national economy. This is why its labour contracts are covered by this (rather obscure to most people) railway act.
It used to be, when times were good, that no one paid much attention to the anti-strike provisions of the act; there was plenty of money to spread around in the happy days of regulation. Now that austerity is the order of the day it has become plain what a 'devil's bargain' has been struck for labour. What was once protection is now oppression.
For an example of what can happen when the rank and file ignore the law in the quest for what 'feels right', just look at the PATCO strike in the States. The air traffic controllers got rid of a union head who advised a 'softly-softly' approach to put a real fire-breather in. He proceeded to take a very popular, confrontational approach to negotiations with the government. Then they finally went on strike, basically daring the government to fire them, which would cripple the US ATC system. Of course Ronald Reagan sacked them all, which crippled the US ATC system but that was okay, because he was able to blame all of that on the stiking controllers whom the White House spin machine made out to be a mob of bomb-throwing anarchists rather than US citizens trying to exercise their right to sell their services for a fair price. That got the attention of some of the other unions, I think.
Of course one could argue that in the world of today there are no more critical airlines. Who would miss one of the majors if they were to go to the wall? And a wildcat strike could be quickly neutralised by other carriers mobilising to fill any gaps in the network. For instance, look at how little missed Eastern was, once it was gone, and yet it was once so large that it was unimaginable that it could be allowed to fail or that it could be so easily replaced. Well, that was then and this is now.
It must be hellishly complicated to work some of these merger deals. I am sure that the beancounters are sat there at a very long table thinking, 'Now remember that the interests of the line pilots come first!' Not.
I remember chatting with a regional airline pilot once when he was trying to explain how he had ended up towards the bottom of the seniority pile after a merger. It all sounded rather depressing to me and was probably one reason why I returned to working in Africa rather than remaining in the States.
I can well imagine someone needing to work as long as possible after getting the short end of the stick, when all that careful planning suddenly goes out the window thanks to the magic of the marketplace. That could well focus the mind on this age restriction.