When Sarah sent Hagar and Ishmael away in Genesis 21, Ishmael is referred to several times as a child:
15When the water in the skin was gone, she put the child under one of the bushes. 16Then she went and sat down opposite him a good way off, about the distance of a bowshot, for she said, “Let me not look on the death of the child.” And as she sat opposite him, she lifted up her voice and wept. 17And God heard the voice of the boy, and the angel of God called to Hagar from heaven and said to her, “What troubles you, Hagar? Fear not, for God has heard the voice of the boy where he is. 18Up! Lift up the boy, and hold him fast with your hand, for I will make him into a great nation.” 19Then God opened her eyes, and she saw a well of water. And she went and filled the skin with water and gave the boy a drink. 20And God was with the boy, and he grew up...ESV
However in Genesis 17:25 when Ishmael was circumcised (3 chapters before), it says he was 13 years old:
And Ishmael his son was thirteen years old when he was circumcised in the flesh of his foreskin.ESV
Was Ishmael a teenager when he and Hagar were sent away by Sarah? Or was Ishmael a child?