People get older and change their views. Real world starts to jade optimism
The truth is actually the opposite. If anything, people tend to become more liberal as they age in some ways, they only become more conservative relative to the rest of society (which has generally liberalized as a whole faster than individual cohorts do).
Basically political ideology tends to change little over time. Whatever beliefs you hold when you're 20 are likely to be broadly similar to those you hold when you're 50. The idea that people become more conservative in absolute terms as they age is not well supported by the data.