While using the game editors, through trial and error, I noticed a curious condition.
I have an scenario in 1950. I created a leader in 31/12/49 so he appears on the scenario. But he doesn't, instead, a leader that is born in 1886.
This means that the leader that appears is not the "youngest" one.
I lowered that older leader birth age to 85,84,83,82,81, nothing. Until I lowered to 1880, finally my new leader appears.
This means that leaders have a "lifespan" of 70 years. If the leader doesn't reach 70 years old, he will appear in an scenario.
Is this true? This information could be of much value for the modding community, as we will understand the game further and make more of it.