1)
Why does the Torah see fit to tell us Avraham's age when he bore Yishmael?
1.
Rashi: To teach us the praiseworthiness of Yishmael, who was thirteen years old 1 when he underwent the Milah, yet he did not object. 2
1
Moshav Zekenim, Riva (both on Bereishis 17:26); Gur Aryeh asks - It explicitly says below (17:25) that Yishmael was 13 when Avraham circumcised him! Perhaps we know that he consented only due to this [extra] verse.
2
Yishmael (who also did Teshuvah - Rashi to 25:9), instilled into his children a streak of religion, something that his nephew Esav did not do.
