Ishmael was about 14 years old when Isaac was born, according to the usual reading of the Genesis chronology.

Quick Scoop

Here is how that number is arrived at, based on the biblical text:

  1. Genesis states that Abraham was 86 years old when Ishmael was born.
  1. It then says Abraham was 100 years old when Isaac was born.
  1. The difference between 100 and 86 is 14, so Ishmael would have been fourteen when Isaac was born.

Some commentators and forum discussions also talk about Ishmael’s age later, when he and Hagar were sent away.
Because that happens after Isaac is weaned (often estimated around age 2–3 in that ancient context), they calculate Ishmael as a teenager of about 16–17 at that point, but still about 14 at Isaac’s birth.

In many current online Bible forums and Q&A sites, people summarize it simply as: “Ishmael was 14 when Isaac was born,” and then debate how old he was when expelled, usually settling in the mid‑teens.

TL;DR:
By lining up Abraham’s ages in Genesis, Ishmael comes out to roughly 14 years old when Isaac was born.

Information gathered from public forums or data available on the internet and portrayed here.