I blame a society that expects increasing solemnity with age. According to these unwritten rules people are supposed to become more planted and mirthless as they age.
It seems that levity becomes conditional as you age; apparently after a certain age, you can only joke among old friends (who are as old as you are), you can joke with little children (who are closely related), you can joke with the spouse (but only on Tuesdays... and then only if it isn't raining), you can joke with the help (if you fancy a illicit hanky panky)... the rules are so bizarre that you'd think I was making this up!
