There is probably one major reason why we don't have 'younger' people going for a role such as being a president and that is experience. They need to learn the ways of politics, how to handle the pressure, how to deal with the public, make mistakes and learn from them to better themselves as politicians and time to prove to their fellow party members that they can do it. And there is only one real way of doing that and that is time.
I'd like to know that a president/ Prime Minister has had some experience in parliament before being handed the job, plus like to see them in the public eye a bit to get to know them and younger people don't often get that sort of coverage on a national scale.
As for values, I think that's the reason why it's good to change president/Prime Minister every so often. For the last 10 years, Aust had a PM who seemed to be stuck in the past with his thinking (from social to environmental issues) and it seemed that Australia was well behind most other countries in terms of thinking and laws.
But I don't thinks most of the older politicians are stuck in the past though, imo they wouldn't get voted in if they were. They are still at the whim of the public, if the public doesn't believe in the values being presented, they won't vote for them (and I think that's part of the reason, Aust kicked out the former PM).
If it's that's much of an issue - why not vote for the younger generation at a local level? (local mayors, candidates, representatives etc - not sure how the system works in America) and that's a start and how they start getting their experience up for the big job.