I feel like it would make sense to implement a mechanic like this (like CK2 has the malus for short reign and whatnot). It'd primarily be for ties in the sense that it was decided for the Habsburgs to retain the throne with their 3 year-old archduke when they were tied with Bohemia's 4/5/3 ruler who was around 30. Surely electors would prefer a strong emperor as opposed to a child whose parent sat on the throne before?