Final answer:
Abram was 100 years old when Sarai bore Isaac.
Step-by-step explanation:
When Sarai bore Isaac, Abram was already an old man. According to the Bible, Abram was 100 years old when Isaac was born. This is mentioned in Genesis 21:5 which says, 'Now Abraham was one hundred years old when his son Isaac was born to him.' So, Abram was 100 years old when Sarai bore Isaac.