For many men in Genesis, ages for becoming fathers and ages at death are given.
However, there are also some rather unique ages given. For example:
Joseph was 30 years old when he entered the service of Pharaoh, king of Egypt Gen 41:46a TNAB
Why might an age like this be given?
Note: Other unique ages given include Ishmael’s age of 13 when he was circumcised (Gn 17:25) and Abram’s age of 86 when Hagar bore him Ishmael (Gn 16:15).