I'd say that there clearly is an externality being addressed by age discrimination legislation. It's not in the interests of the state to have corporations pus

I'd say that there clearly is an externality being addressed by age discrimination legislation. It's not in the interests of the state to have corporations pushing down wages by favouring only younger staff. Low wages == low tax receipts, which is objectively bad for countries and their citizens. Also as citizens it's hardly in the interests of the group as a whole in allowing corporations to drive down salaries and make older citizens redundant. Every young citizen who might benefit from such actions now will become an old citizen who will get the downside later in life. At the moment we're discussing the behaviour of a large corporation (google) so it makes sense to address that class of company. To be clear, I don't hate corporations at all, but nor to I have any faith that they'll always act in the best interests of the country I live in, in fact I expect them not to do so where their interests diverge from the interests of the country and so I expect my government to address that with legislation.