1 Kings 3:7

Iam but a little child This is a form of expression meant to indicate want of experience, but cannot be pressed literally. What Solomon's age may have been we have very imperfect data for judging. The ordinary chronology puts the murder of Uriah about twenty years before David's death. If this be correct Solomon might be at this time 17 or 18 years old. Bunsen (Bibelwerk) says 22.

to go out or come in This expression of going out and coming in is frequent in one form or another for the manner of leading one's life, and engaging in one's proper duties. So Joshua uses it (1 Kings 14:11) of his fitness for the leadership of Israel. Moses (Deuteronomy 31:2) when he is speaking of his growing age, says he can no more go out and come in.