Lots of factors. Puberty is measured in males by more than pubic hair. Testicular & phallic size, muscle mass, facial & abdominal hair all are signs of a maturing male. Your genetics also play a powerful role in when you go through puberty & how fast you do it. Genes also determine how hirsute (hairy) you will be. Remember, men can grow, not only in size, but in secondary sex characteristics, until 21 yo.
Depends on family. The amount of pubic hair, body hair, and facial hair a teenager gets (and when he gets it) is mostly genetically determined. That means he will likely follow the pattern of his father and older brothers. So, he should talk to his doctor if his brothers and father had lots of pubic hair by age 16, yet he himself has little or no hair. Annual check-ups are needed for following puberty changes.