Age of Gideon's son

Question

I know in biblical Hebrew that age of boys and girls was often determinable by the word the author used. In Judges 8:20 we read about Gideon's son Jether being afraid to murder Zebah and Zalmunna because he was still a "young man".

How old would Jether have been?

Judges 8:20-21 So he said to Jether his firstborn, “Rise and kill them!” But the young man did not draw his sword, for he was afraid, because he was still a young man. Then Zebah and Zalmunna said, “Rise yourself and fall upon us, for as the man is, so is his strength.” And Gideon arose and killed Zebah and Zalmunna, and he took the crescent ornaments that were on the necks of their camels.<

naar (נַ֫עַר)

Answer 1

It would be hard to determine Jether's age based solely on the word naar. As mentioned in another answer, it refers to Moses when he was only a few months old (Ex. 2:6). It also refers to Joseph when he is 17 years old (Gen. 37:2) and again when he is 28 years old (Gen. 41:12).

Answer 2

naar is equivalent to our English word "boy".
It can refer to a male anywhere between the age of infancy (Exo 2:6) to before marriage. It denotes that the person is not mature yet.