If youth but had the knowledge and old age the strength.

Related:

• Forty is the old age of youth; fifty is the youth of old age.
  Victor...
• Old age and treachery will overcome youth and
  skill...
• Rashness attends youth,
  as prudence does old age. --...
• Youth is a blunder, manhood a struggle, old age a regret.
  Benjamin Disraeli,...
• Youth is a blunder; Manhood a struggle; Old Age a regret.
  Benjamin...
• An old cloak makes a new jerkin. --
  Age-old English...
• Middle age is youth without it's levity. And old age without decay.
  Daniel...
• A wise man is strong; yea, a man of knowledge increaseth strength.
  Old Testament -- Proverbs xxiv,...