People get more conservative with age. A lot of conservatives attribute that to people wanting to get back to basic morals, but I attribute it to people getting plain old sick and tired. People tend to think the world is constantly getting more difficult and corrupt, that their childhood was a golden era for humanity, that the world is going to hell on a very clear path.
To me, remaining liberal is more akin sticking to your basic morals, or at least to my morals: of being open-minded, sympathetic to the less fortunate, of doing unto others as you would have them do unto you.
The older I get, the harder it is to stay that way, because the older I get, the more exposed to crap I am. It gets harder and harder not to say, screw everyone, I work damn hard and I should only worry about myself and hold onto mine and let the weak be damned.