How old was Isaac when he was weaned, and how old was Ishmael at that time?

Isaac was five years old when he was weaned, and Ishmael was about eighteen or nineteen years old at that time. Since Ishmael was born earlier to Hagar, he was no longer a little child but at the end of his teen years.

Les explains that chronologically Isaac had to be five years old when he was weaned, which puts Ishmael at about eighteen or nineteen. Ishmael was not a little child anymore but was at the end of his teen years. This fits the account where the child grew and was weaned, and Abraham made a great feast the same day that Isaac was weaned.

Genesis 21:8

And the child grew, and was weaned: and Abraham made a great feast the same day that Isaac was weaned.