Man child

[Tina]

a grown man who is very immature, therefore considered a man child.

[Tina]

A man child is a male who is over the age of 25, who still lives as though he is a juvenile. Many man-children are not gainfully employed, and survive off of the financial support of their enabling parents. Heavy video-game addiction to fantasy games such as World of Warcraft are key to the man-child.

[Hina Muqadas]

A man with the character of a young child. Also could be a juvenile who is too young to be old, but too old to be young. An old soul trapped in the body of an adolescent. A man who is too old for babysitting, but desperately needs it.
plural: manchildren

[Justin Bieber]

A man by age but a child in mentality and actions. Usually an inability to get over the frat boy or party boy phase. Cant have fun without a beer; oftentimes brews his own beer. Still relate to women as sex objects (even in theyre married) and are emotionally undeveloped (e.g., fight for their rights mentality even if there is nothing worth fighting; rarely takes responsibility for own failings). A general irritant to women and men that have matured.