I've also noticed that it is always said from old conservative people to young liberal people. In other words, it's something that old conservatives tell young liberals (and tell themselves) to justify the fact that they have changed as they've aged.
It's also pretty patronizing.
Because what I actually hear is this: "well, you're young and emotional, I am sympathetic to your childish feelings. But when you grow up and think about things more, you'll be like me."
How many times does one change in this regard? Because I started out very young as a conservative. It's what I was taught to be. And then in my mid-twenties I became liberal, because I learned more about the complexity of the issues and the world. When my parents were the age I am now, they were conservative... so did they get 'old' prematurely? Or do I get to qualify as 'old' in spite of my liberalism? I wonder, at what point will I be 'old'? President Obama turns 51 this year, and he's liberal. Sarah Palin is three years younger, but she's conservative.
Let us be logical here, political beliefs are not a product of age. They are the product, I think, of priorities. Consider, for example, the simple matter of finance. The average young person has very little money, and might naturally be in favor of things like economical stimulus programs and wealth redistribution. The average older person has significantly more money. They have probably worked hard for it, and they feel entitled to keep it rather than be obligated to share it. So they want to get rid of taxation on capital gains and estates.
A younger person--a poorer person--may be more likely to need assistance from welfare, whereas an older person is more concerned with investments, property taxes, and social security. This is all rational, I don't think less of a person for having different priorities than my own. I do get a bit miffed when they belittle my priorities or (especially) my intelligence.
Please, do tell me what you believe, and why. Tell me why it's important to you. I do care, and I am interested. If you can, give me statistics to back it up (because I find facts to be remarkably convincing). From time to time, new information leads me to change my perspective (that would be how I became the liberal I am today in fact).
But don't pat me on the head with a patronizing "Mother knows best" attitude. Do not belittle me, my mind, or my abilities in that way. Trust that I am capable of feeling--and thinking--rationally and responsibly.
Be willing to appreciate that we can have different interests and priorities, and that that's ok. We can still respect each other. Let's just stop pretending that our differences are a product of maturity or intelligence, because they aren't.