During which year Emperor Shapur II learned to play polo?

Context: The game's English name derives from the Balti language, from its word for 'ball', polo. It is cognate with the Standard Tibetan pulu, also meaning 'ball'.

Although the exact origins of the game are not certain, many scholars suggest it most likely began as a simple game played by Iranic and Turkic equestrian nomads in Central Asia. An archaic variation of polo, regionally referred to as buzkashi or kokpar, is still played in parts of Central Asia. It was developed and formalised in Ancient Iran as "chovgan", becoming a national sport played extensively by the nobility. Women played as well as men. During the period of the Parthian Empire, the sport had great patronage under the kings and noblemen. According to The Oxford Dictionary of Late Antiquity, the Persian ball game was an important pastime in the court of the Sasanian Empire. It was also part of the royal education for the Sasanian ruling class. Emperor Shapur II learnt to play polo at age seven in 316 AD.

Answer: 316 AD