you can't put an old head on young shoulders

"Young men will be young men; you can't put an old head on young shoulders," he added, repeating trite sayings as if they were original with himself.

1901, Pauline E. Hopkins, Hagar's Daughter, ch. 25 (Google preview) (in The Magazine Novels of Pauline Hopkins, Oxford, 1990)

The one knock against Bobby is that he is not great defensively. I think that's a valid criticism, but not altogether fair. You can't put an old head on young shoulders.

1970 April 1, Punch Imlach, “In crystal ball, Bruins get nod for first place”, in Windsor Star, Canada, retrieved 11 Dec 2012, page 33

"All of a sudden they are now short of experience in the centres and wing. As the old saying goes, you can't put an old head on young shoulders."

2010 December 14, Dean Ritchie, “Gutted Eels are left reeling”, in Herald Sun, Australia, retrieved 11 Dec 2012

In those days I looked down on Stephens and repeated Russell's verdict with derision; which shows not only that you can't put an old head on young shoulders but that you shouldn't try.

2011, Frank O'Connor, “Introduction to A Portrait of the Artist as a Young Man”, in The Best of Frank O'Connor, →ISBN, page 183