Just as a thought, there have been games I played where aging stops at a certain age. Everyone ages to a certain age and then they stop. Death is caused by war, disease, disasters. Personally, I like just spending time in games like Warband and Bannerlord. The aging factor kinda ruins that.
A second option might be something like Story Mode and Sandbox Mode.
Story Mode can have linear quest. Sandbox, no story driven quest, only quests to fight bandits, rescue specific person, find lost item, and so on. Then you can play as a mercenary or try to run your own kingdom.