I think it's a plain human function really. The older you are, the less able you are to form new opinions about things. Look at how easy it is for young people to learn a language, but old people never exceed a certain level when they try. So, old people want to stick with what they knew and got used to.
BTW, I'm talking here more about "liberal" and "conservative" in a very generic sense, not so much specific manifestations of them in politics. That is, for my comment here, there are conservative liberals in the sense that they will always vote liberal, just because that's what they've been doing for the last 20 years.
rumborak