In Austria, for most professions, there are contracts that explicitely require wages to increase with experience (number of years worked). This means that older employees are automatically more expensive. It's especially bad for many "public" positions; for example, a teacher's salary automatically increases every two years or so. A 65 year old teacher earns twice the salary of a 25 year old teacher. Sure, the older teacher has more experience, but it's hard to argue that experience is worth more than TWO young teachers.
Also, often retirement is just a convenient way to get rid of people. If everyone's goal is to keep climbing the ladder, we have to get rid of the people at the top at some point. There's only so much space up there. And since the people at the top probably don't want to switch to roles with less responsibility, the only place left is retirement.
And last but not least, willingness to change is also necessary. Now, I don't think that a 60 year old is per se more reluctant to change than a 30 year old. I think that senior people can adapt to changes just as well as young people; given the right motivation. However, a 30 year old has a lot more extrinsic motivation to change than a 60 year old: when you are young, you have to adapt, or you will end up poor. When you are old, you have the option to refuse to adapt and just retire...