ESV wrong again...

The ESV  has Saul being one year old when he became king:

Saul lived for one year and then became king...1 Samuel 13:1 ESV

The ESV says in 1 Samuel 9:2, along with chapter 13 verse 1 (above) that Saul was a really huge one year old:

 And he had a son whose name was Saul, a handsome young man. There was not a man among the people of Israel more handsome than he. From his shoulders upward he was taller than any of the people.

Wow.

The KJV sets the record straight:

Saul reigned one year; and when he had reigned two years over Israel, ...1 Samuel 13:1 KJV

And he had a son, whose name was Saul, a choice young man, and a goodly: and there was not among the children of Israel a goodlier person than he: from his shoulders and upward he was higher than any of the people. 1 Samuel 9:2 KJV

Manuscripts and the quality of translators do make a huge difference...