Gerontocracy is literally, rule by the old ones.
Modern Medicine and nutrition has extended the life span of Cardinals to a much greater extent, than it has managed to extend the agility of their minds. In fact if anything it is now more likely that an aged Cardinal would have significantly diminished mental capacity, given their increased average age.
The Christian Faith has had an extraordinary impact on Civilisation and the formation of modern Society. Yet a cohort of yet older and older men are in control of the moral teaching and values that that Church teaches, and which is still such a big influence on modern Society despite the inclination towards Secularism.
I don't suggest that old men should not be Cardinals, but that it might be desirable if they became Cardinals much earlier in their lives. This might to some extent go some way to balancing the rising age profile of the body of Cardinals.
There must be men in their thirties or even forties who are capable of becoming Cardinals! There are probably even women who could do the job.
Are younger candidates not capable of being guided by divine inspiration?