Children die of old age before parent.

I’m playing the 100 baby challenge and its against the rules to edit the lifespans. I just recently installed the game and never fiddled with the settings, so all settings are the original ones. Now my question. When I move my young adult children out of the household I usually move them into one of the neighbouring homes. My matriarch (the mother of what will hopefully be 100 babies) is an adult and her second eldest son just died of old age. Her oldest son is and elder. All of her lovers also die of old age. 

How come everyone outside the household ages so much faster? Its really annoying that her children die of old age... why do they do this? and could I change this? (preferably without breaking the 100 baby challenge rules) 

Thanks in advance 🙏