The traits the word 'childish' addresses are seen so often in adults that we should abolish this age-discriminatory word when it comes to criticizing behavior associated with irresponsibility and irrational thinking.
But thy strong Hours indignant work’d their wills, And beat me down and marr’d and wasted me, And tho’ they could not end me, left me maim’d To dwell in presence of immortal youth, Immortal age beside immortal youth, And all I was, in ashes. - Tithonus
Every one of course represents the spirit of his age, but there is an eternal aspect of the Spirit of every age which may be caught. To recreate the past from the mutilated fragments of the present is the task of the Historian.
There are many mysteries in old age but the greatest, surely, is this: in those adverts for walk-in bathtubs, why doesn't all the water gush out when you get in?