I'm in my 40s, and I have only gotten more and more progressive as I've "grown up".
You want to know why?
Because I've met more marginalized people. When I was 16, I didn't know anyone who was openly queer, and I lived in a moderately-affluent, nearly-all-white area of the US.
Now, I know many people who are queer, poor, disabled, and/or people of color, and because I was raised to care about people and believe to value every human life, I want them to be treated as well as I (a middle-class, white, straight, cis man) am.