Sarah and her husband are hoping to have a boy. They already have three girls.
Ahmed and his wife have three little boys under the age of five.
Hector wants to join the military but he’s still a boy. He has to wait until he turns 18.
Two teenage boys got lost in the forest; they were found and returned to their families.
When I was a boy, I played baseball with my friends almost every day in the summer.
He’s a little boy.
In some situations, the word "boy" is used in reference to a man:
The boys in the office are working through the night.
Okay boys, let’s go get something to eat.
Bobby is a good ol’ boy. (good old boy is a term used to describe a man who lives in the south or in a rural area.)
You can tell that Carl is a part of the old boys network. (The old boys network is a reference to men who are in control of a particular situation, organization, business, etc. It’s not an actual network.)
He’s part of the old boys network.
The word "boyfriend" is used for a romantic relationship. This word can be used for a boy or a man of any age.
Tracy has a boyfriend.
Olivia divorced her husband two years ago, but she has a new boyfriend whom she might marry.
How many boyfriends have you had?
The word "boy" can be used as an interjection.
Oh boy! We’re going to get a puppy.
Boy! Something stinks!
Boy oh boy! You’re in trouble.
The use of "bad boy" has recently become popular when referring to a thing. This is a type of slang, but it’s not easy to use.
Okay, let’s fire up this bad boy and get going. (bad boy = a cool car)
You got a new computer. Let’s have a look at that bad boy.
He’s a little boy. 
He’s part of the old boys network.