The answer to this question has (again) to do with the argument vs. adjunct distinction. Often the term complement is used in place of argument, although the argument notion is more clearly defined. Arguments are usually noun phrases (NPs), whereas adjuncts are typically adverbs, prepositional phrases (PPs), or clauses. Sometimes, however, PPs and clauses can be arguments instead of clauses, and on occasion an NP can be an adjunct instead of an argument.
The example sentence in the question contains the NP his entire life, which is an adjunct as opposed to an argument. The question calls it an adverb, although that term is less precise. For me, an adverb is a single word that functions as an adjunct (e.g. really, probably, quickly, willingly, etc). Hence I would not call his entire life in the example sentence an adverb. I would, rather, call it an NP that is functioning as an adjunct.
As stated, NPs are usually arguments, not adjuncts. There are certain uses, however, where NPs clearly function as adjuncts. A common such case is when the NP expresses time duration, e.g.
She slept all day.
He worked the entire afternoon.
He stayed the whole year.
The NPs all day, the entire afternoon, and the whole year are adjuncts; they express the duration of the event or action expressed by the verb. We know that they are adjuncts in part because they can be omitted without altering the basic meaning of the sentence:
Another, similar use of NPs as adjuncts occurs with expressions of distance, e.g.
She drove the bus ten miles.
They flew two thousand miles over the ocean.
The NPs ten miles and two thousand miles are adjuncts. We know that they are adjuncts in part because they can be omitted without changing the basic meaning of the sentences:
She drove the bus.
They flew over the ocean.
Languages that have case such as Latin and German mark these NPs with the accusative, e.g.
Sie hat den ganzen Tag geschlafen.
she has the-acc. entire day slept
'She slept the entire day.'
The NP den ganzen tag 'the entire day' is marked accusative, which is an indication that it may be functioning as an adjunct (and it is).
Recognizing NPs that are adjuncts may be somewhat tricky. It's easier to recognize PPs and clauses that are adjuncts, however, because these categories are typically adjuncts rather than arguments.
To build an understanding of these matters, it's beneficial to read what one can find about the argument vs adjunct distinction. Wikipedia is a place to start: https://en.wikipedia.org/wiki/Argument_%28linguistics%29, https://en.wikipedia.org/wiki/Adjunct_%28grammar%29, https://en.wikipedia.org/wiki/Complement_%28linguistics%29.