Against Common Sense: Younger People Are Not More Liberal

  Now it is a common notion that the younger a person is, the more he tends to be liberal in his politics. So the corollary is in fact, that older people are more conservative. And seeing as that statement has the logical force of a biconditional, it follows that if one part of the statement is wrong, then so is the other. And I think that the atomic sentence "the younger is the more liberal" is the false one.
  How can this be? Firstly, if the above common notion is true, then one encounters a problem in the case that someone turns 50 -will he be equally liberal and conservative? But secondly, life expectancy was lower in the past, and equivalently the probability of reaching old age was lower than our own. So (all things being equal) there were more young people around in the past. And yet we see that the past was significantly more conservative than today such that anyone is not only conservative but reactionary who wants to turn back social mores to 1500AD.
   Finally, then this is a contradiction and as such it makes it false that younger people are more liberal than older people and false that older people are more conservative than younger ones.