at the age of puberty , that is between 8 and 16 , most likely to grow facial hair is at age 13-14 or sometimes even 12 . its when you hit puberty (changes to body)
Usually, puberty for a boy ends when they are about 18 or 20 years of age.
During puberty, hair will grow around the anus and on the buttocks themselves, along with growing on the testicles, base of the penis and around it.
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Girls usually start puberty before boys...girls start pre-puberty around the ages of 9 to 11 and puberty around 12 just like boys do.