Maybe some workers 50+ are truly past it or so set in their ways that they're not adaptable to the dynamics of IT these days. But mostly when you get rid of older workers, no matter how 'gently' you do it, or how gracious you try to be, you end up losing a lot of talent and experience. You don't just shuck the people that know where the bodies are buried (though maybe that is part of the intention), but the people that understand why decisions were made that seem illogical on the surface, without context. So you end up making the same mistakes that could have been avoided if anyone was left to remember the ordeals of the past. You truly end up stepping over dollars (or pounds, or yen) to pick up pennies, for a short term unsustainable gain, and besides the human harm, you truly hurt the business IMO. Not that there aren't a few crusty old bastards in every organization that only contribute friction and frustration to others.
There is a reason that every indigenous peoples in every land revered their elders and kept them around despite their apparent burden on the younger folk. And its name is wisdom, which is not obvious to 20-somethings that "know it all" despite having experienced very little overall.