National or country leaders must not be older than 65 years, and must have children.
People over 65, with rare excptions, have the most energetic part of their life behind them. They are more suited for fishing than for managing a local community, let alone an entire country.
You remember situation when highly ranked EU official arrived to a meeting, and his assistant warned him that he had two different socks on his legs. They tried to resolve it discretely, but it leaked out. He cannot manage to dress himself properly, so how can you expect him to manage lives of millions or even billions of people?
Generation gap is inevitable at that age; a person in their seventies cannot understand the behaviour, motives and goals of people in their mid-age, who contribute most to the economy, and young people, who will inherit the Earth.
People of that age, with their health and sanity preserved, could serve as counsellors – surely, they have immense experience and they have something to say, but the final decision should be left to those who have prospect of consciously shaping this planet more than a decade.
You had your fair share of life, and now it’s time to step off, and let people in their zenit decide of their lives!
As for childrenless leaders, again with rare exceptions, their interests hardly shoot longer than for their own benefits. Whether we want to admit it or not, none of us will live forever, and this world will remain to our descendants. The one who does not have their own descendants, cannot trully care of ones of other people.