Late onset of puberty in the male is defined as
"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
Puberty onset after 16 years
Puberty onset after 17 years
Puberty onset after 18 years
Puberty onset after 21 years