Dating frat boys
The word "boy" comes from Middle English boi, boye ("boy, servant"), related to other Germanic words for boy, namely East Frisian boi ("boy, young man") and West Frisian boai ("boy").
Although the exact etymology is obscure, the English and Frisian forms probably derive from an earlier Anglo-Frisian *bō-ja ("little brother"), a diminutive of the Germanic root *bō- ("brother, male relation"), from Proto-Indo-European *bhā-, *bhāt- ("father, brother").
Thus the compound -man can then be replaced by -boy, as in footboy; or boy is simply added, either as a prefix (e.g., in boy-racer) or as a suffix (e.g., in Teddy Boy).
An adult equivalent (with or without -man) is not to be expected when -boy designates an apprentice (for which some languages use a compound with the equivalent of boy, e.g.
"the boys at the office, - police station etc." (often all adults).
In some traditions boyhood is held to be exchanged for adult manhood, or at least approach it significantly, by certain -in se independent- acts assuming a role deemed to be typical for a "normal" man (though there are limits) as marriage, fathering offspring or military service.
Various cultural and/or religious rites of passage serve, partially or specifically, to mark the transition to manhood.
In US urban slang, particularly in African American and Latino slang, the term boy is used with a possessive as meaning friend (my boy, his boys), presumably as a reduction of homeboy, originally a male from the same area.
In some cases, the word boy is used merely to designate the age of the (male) person, irrespective of the function, as in altar boy, a minor acting as liturgical acolyte, or in Boy Scouts, an organisation specifically for boys.
A young man who has not assumed (or has been denied) the traditional roles of a man might also be called a boy.