A man is an adult human of the male sex.
The term man people usually mean a grown man, as it is, at least physically, has developed at puberty. For persons under 20 years, the terms 'man' and 'woman' rarely used in everyday speech. [Source?]
A boy is a male child. Many associate the word man with a certain sense of responsibility that younger men are not ready for, others feel just too old to young to be called. That is often a reason why many people use terms neither a young man to denote: estimating the age and level of responsibility are factors that the use of the terms boy or man Miserable. Some people therefore prefer the word man, a term used between men indicated that sit at the end of puberty.