How is this even a debatable question? I would love to see one argument for "no" explaining how liberals are not mostly young people. Why are most young people liberal? Statistically speaking, Liberals tend to be overall smarter than the conservative side. Therefore, many young people
think that being labeled as a liberal will suddenly make them smarter and better than those evil, hateful, and ignorant conservatives. I know this is quite off topic, but if you want to be smart, just work hard. Don't be part of a group of relatively smart people, that won't make you smarter. It will only hurt the group's reputation...
Liberalism is something that is embraced by younger people. Winston Churchill said "if you are not a liberal at twenty you have no heart, if you are not a conservative at forty you have no brain". Liberalism is a bleeding heart philosophy that bodes will with the younger demographic. They are the progressive ones.
Younger people are more apt for liberal thinking thanks to a natural rebellion against authority. Of course that means most liberal voters are younger. It's just a natural way of expressing one's views. As the younger generation grows up and becomes more set in their ways, liberal voters may turn more conservative.
It seems to be the way nature works, the younger people adopt to more liberal ideas and then get conservative over time or the once liberal ideas they supported seem to be conservative after some time. This is nothing new and will be like that forever. That does not mean that all young people are open to liberal ideas or all old people are conservative but the majority behaves and votes that way.
There are older liberals, make no mistake, but the percentage that is under 30 dwarfs conservatives. The reasons for this are pretty simple, the conservative agenda is based on ancient politics that are dying off along with a majority of those that support it. The liberal agenda is far from perfect but it's still the more appealing option for people just getting into politics because it isn't as boastfully hateful as the alternative.
The question is asking whether most liberals are young, not whether most young people are liberals. According to the Census, only about 15% of voters in 2012 were less than 30! Considering that liberals make up maybe 50% of the population, even if all young people were liberal, young people make up nowhere near the majority of liberals!
By the time I responded to this five people had answered yes to this question and no one had answered no. Five people. This is why we have bad policies; people don't think.