When Yitzchak was five years old [(this is Year 2053)] he sat with Yishmael [(who was then nineteen years old)]. And Yishmael took the bow and said he would shoot Yitzchak. Sarah saw and said to Avraham, "Cast out this handmaid and her son," etc. And Avraham rose early and took twelve loaves of bread and a skin of water and sent Hagar and her son [(Sefer HaYashar)].

Some say that this is when the Akeidah occurred [(see Ibn Ezra on Parshat Vayera, see Years 57 and 50, and this requires investigation). And in the Seder HaKabbalah it is written that Yishmael was fifteen years old when he made shade and mocked and worshipped idols. At the beginning of the Shir HaShirim commentary, the Yefeh To'ar wrote that this is not exactly so, but rather means that fifteen years had already passed, thus he was seventeen years old, for he was circumcised at twelve, plus one more year until Yitzchak's birth and two years until his weaning, and this event was after the weaning of Yitzchak.

And in Pirkei DeRabbi Eliezer it says he was seventeen years old. See Yefeh To'ar on Vayera, chapter 12, section 17. And in Pirkei DeRabbi Eliezer and Midrash Shemot at the beginning of Shemot it is written that when he was twenty-six years old he went out to bad culture, which is Year 2062, see there.].