Personally, I think age limits are a good thing with politicians. It is the easiest way to reliably filter out people who are losing their ability to represent their constituents - due to mental stratification, cultural calcification, becoming a known element for horse trading, or decreasing vitality for getting things done.

Sure, we would lose the occasional good person such as Bernie - but in exchange, we least ensure that politicians are aware of the world, and are able to interact with it at a decent speed.