How old was david when he was anointed by Samuel?

How old was David when he was first anointed by Samuel at Jesse's. How many years was David being chased by Saul. What was the age of David when he became King over Judah and Israel.

According to the sub-commentary in the KJV Life Application Study Bible for Psalm 27:14 suggests that David was 16 when he was anointed by Samuel at his father Jesse's house and became king at the age of 30.