Men are men. The term "man" is commonly used for adult males, while the term "boy" refers to a common term for boys or adolescents. However, the term "man" is sometimes used to refer to men, regardless of their age, such as "men's Basketball".

Like most other male mammals, a person's genome usually inherits the X chromosome from his mother and the Y chromosome from his father. Male fetuses produce more androgens and less estrogen than female fetuses. The difference of the relative content of these sex steroids is the main reason of the physiological difference between men and women. In adolescence, hormones that stimulate androgen production lead to the development of secondary characteristics, and therefore show greater differences between genders. However, there are exceptions for some transgender and bisexual men.