We have a system that works well, and has a long tradition. As a general social rule, the age of something is the average number of years it has left. So if a company, or a country is a year old, it has an average of one year more of life. Some will live for another hundred years, and then have an average of a hundred more years of life.
The reason that works is that survival and traditions set patterns that keep going.
Anyway, those are the same traditions that trump is trying to replace with veneration of a 78 year old man. If our country is a personality cult of a 78 year old man, then we have a few more years at most left. donnie jr would never be able to take his father's place.