Confucius. Book 2, Chapter 4.
Book 2, Wei Chang
1. The Master said, "At fifteen, I had my mind bent on learning.
2. "At thirty, I stood firm.
3. "At forty, I had no doubts.
4. "At fifty, I knew the decrees of Heaven.
5. "At sixty, my ear was an obedient organ for the reception of truth.
6. "At seventy, I could follow what my heart desired, without transgressing what was right."
Text source: Lun Yu, The Confucian Analects. Translated by James Legge.