A is for Age of Candidacy

I'm going to focus mainly on the ages required to be on the ballot for national and local elections. There are so many other things you could run for-governor, senator, representative, delegate, deputy, parlimentary member-but I don't think either one of us really wants to read through all of  those. Also, if I don't mention your country and that bothers you, please leave a comment below so I can improve my post.
In America, where I happen to live, you have to be 35 to be on the ballot for president, 30 to be a senator, and 25 for a representative. I always thought that sounded just and logical enough. Forget experience and wisdom, most people in their twenties are busy with other things. College, starting a family, finding and working a good job. Rules aren't so strict for mayors, there have been some young as 18 for small towns.
 But as it turns out, the land of the free and home of the brave actually has required ages years beyond those of many other countries.
Italy has the highest age I could find-50 to run for president. That's 40 for Germany, 35 in India, 30 in Colombia, and 23 in France. Now where did they get that number?
18, age of majority and age of suffrage in many countries, is also old enough to get you on a ballot for a position at any level in Australia, the Netherlands, and the UK minus Northern Ireland. Other countries have it as a partial. In Canada, an 18 year old can run for anything but the Senate. Germany allows them to run in national, regional, and local elections. France's rule lets them compete in "municipal, cantonal, and regional" elections.
But not president. Oh well, wait five years and take it from there.
Now, running and winning are very different things. But it's hard to win if you can't get on a ballot, though I've heard of youth succeeding as write-in candidates.
Which provokes a question-could the United States voting age stand to be lowered? What about those for other countries?
Personally, I say we wait until there's a stream of really promising candidates below the required ages. America has never even had a president younger than 44 (John F. Kennedy). Nobody particularly cares about congressman, so any fuss will probably wait until we elect a 36 year old president.