What term can be used for an adult, Particularly a man, that's in his forties and however behaves similar to a teenager, shunning tasks common of mature folks, preferring to get pleasure from himself? I will concede this answer lacks a few of Whatever you're immediately after - i) it's gender independent, ii) I commonly associate the time period

No, probably not. You will find a estimate I have heard quite a few moments but can't really place my finger on that addresses this, that criticizes English and its puritanical record as leaving it sorely missing in sufficient terminology for these kinds of issues, Therefore forcing English speakers to make use of infantilizing misnomers like "boyf