why do so many people act like children?

Why do so many people act like children I mean seriously lol.

 
        Simply a Rose to brighten your day,
        And maybe lessen the cares in your way;
        And also, too, to help you to know,
        That in knowing you, many others grow!
 
 
 
Because many of them are children either because of age or mentality.

As to opinion/Advice:

o·pin·ion (ə-pĭn'yən)
n.

A belief or conclusion held with confidence but not substantiated by positive knowledge or proof: “The world is not run by thought, nor by imagination, but by opinion” (Elizabeth Drew).

A judgment based on special knowledge and given by an expert: a medical opinion.

ad·vice (ăd-vīs')
n.

Opinion about what could or should be done about a situation or problem; counsel.

The reason I feel that most if not all are afraid of getting old, It's the need to be young again, vibrant and full of life. It's the fear of losing our attraction to the opposite sex and not being desirable enough to be loved or needed. Fear and loneliness are the most common reasons for acting childish with an air of careless abandon that only a child can truly know.