From 《
后汉书·
马援传》, the biography of Eastern Han general Ma Yuan (14 BCE-49 CE): '
丈夫为志,
穷当益坚,
老当益壮' — 'A man's resolve should grow firmer in adversity and stronger in old age.' Ma Yuan led troops into battle in his sixties; the phrase became the canonical praise for vigorous elders.