For men, facial hair growth, such as sideburns, tends to grow around the age of puberty. In general, this could be around 15 or 16 years old. It may take some years more before they can grow a full beard.

Does sideburns count as a beard?

Sideburns can be worn and grown in combination with other styles of facial hair, such as the moustache or goatee, but once they extend from ear to ear via the chin they cease to be sideburns and become a beard, chinstrap beard, or chin curtain.

At what point does facial hair become a beard?

It is typically a secondary sex characteristic of human males. Men typically start developing facial hair in the later stages of puberty or adolescence, around fifteen years of age, and most do not finish developing a full adult beard until around eighteen or later.