The average age for a boy's voice to change is around 12 years old.
A boy's voice begins to change from their child voice to adult voice around 12 years old and they usually have a harder time talking because of the voice cracking and sounding different.
This can be embarrassing for kids especially in school but it's a normal thing that all boys go through and eventually the cracking of the voice will stop once the boy's voice gets to where it should be.
The voice is usually fully changed by age age 15 to 16 depending on the boy.
When a boy goes through puberty that is when the boy's voice begins to change and it can begin as early as age 10 but most commonly it happens around 12 years old.