In the famous 1952 film 生きる (Ikiru), the government-office employees frequently use 僕 to refer to themselves (even the female character used it). Based on this understanding of 僕, 僕 is basically a pronoun which boys use; but that doesn't explain this frequent use in an office. This formal definition mentions a social status element ("対等またはそれ以下の人に対して用いる。") but isn't very clear on exact situations.
In what situations would 僕 be used outside the context of boys? In what professional or social situations would it be appropriate and natural for an adult man to use, as opposed to 私?