It has been said that the transition from childhood to adulthood occurs at the moment one becomes conscious of one’s own mortality, but perhaps it would be better said that one’s maturity is proportional to one’s cognizance of one’s mortality — for such awareness is not a binary division, but a position along a continuum.
It should come as no surprise that the older are generally more mature, for their knowledge that death is ever more imminent brings them to see death as the pre-eminent property of human life.