This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Late onset of puberty in the male is defined as 
Select and explain. 
A. Puberty onset after 16 years, B. Puberty onset after 17 years, C. Puberty onset after 18 years, D. Puberty onset after 21 years
A: Puberty onset after 16 years
Answer: A: Puberty onset after 16 years 
Explanation: "The diagnosis of delayed puberty is made when signs of sexual development, such as an increase in the volume of the testis are not evident even by the age of 14years in boys and breast budding by 13 years in Girls".
Some important causes of delayed puberty

Hypothyroidism
Hyperprolactinemia
Noonan syndrome
Klinefelter syndrome