John Gill Commentary 2 Kings 22:1

"Josiah was eight years old when he began to reign; and he reigned thirty and one years in Jerusalem: and his mother`s name was Jedidah the daughter of Adaiah of Bozkath." — 2 Kings 22:1 (ASV)

Josiah was eight years old when he began to reign
And must be born when his father was but sixteen, for Amon lived but twenty four years, (2 Kings 21:19) ,

and he reigned thirty and one years in Jerusalem ;
and so must die at thirty nine years of age:

and his mother's name was Jedidah, the daughter of Adaiah of Boscath ;
a city of the tribe of Judah, (See Gill on Joshua 15:39).