This mod doesnt do that. You might be thinking of the Max Skills mod. Checked it out and it seems to be a UI limit. When the nobles reach 16 it removes the button.

How exactly can you start with more than 16 characters if you set the setting past that, when the plus disappears in the starting menu after you have 16 characters on board?

Its doesnt. This allows for more range in the current settings.

Does this let you increase/remove kingdom size limit?

could you make a mode that ignore or turn off the age + age defuff , so the noble will not die from old ?

Possibly, it would be a new mod if so.

Could we get an immortal leader setting? That would be wonderful.