Learn English – How many years (have you studied)/(have you been studying) English

I think your questions are both OK. Your only mistake is that you mention the Present Perfect Progressive (also called the Present Perfect Continuous) but you don't use it.

When inquiring about periods of time regarding activities that still occur/are still true (and are not completed), the right approach in English is always a Present Perfect tense. Whether that be Continuous (+ing) or Simple (+ past participle) (and if the action is completed, but we don't know when), depends on the verb. State verbs (like "be" in your first example) can only be employed using Present Perfect Simple, whilst action verbs (like "study" in your second example) can be employed in PPS/PPC. Using PPC gives your sentence/question that emphasis of "repeated/continuous" activity, but is not mandatory. So:

How long/How many years have you studied English?

Is just as worthy as:

How long/How many years have you been studying English?

(The same applies to your first example too)

Which brings us to your question of how to phrase your query if you wish to receive an answer using a specific "time reference" (ie "years" in your example). Generally speaking, the native English speaker will likely not worry about the "time" part of the question too much, leaving the listener to respond in the most logical way. In your example, this would likely be in years, or possibly:

Since I was 5.

Of course, sometimes specificity is needed or desired as in your question. If you don't want "since I was 5" type answers, then you need to "lead" the listener, by encouraging them to respond according to the "time" part of the question you use.

How many years? = For x years

How many days? = For x days

Etc.

Consider this last example of a situation where a specific (maybe overly?) response is needed.

A manager has to enter a candidate's information into the following box on their computer during a job interview: Years of higher education studies completed: [ ]

The manager will obviously require a response in years, and so will need to ask his question accordingly:

How many years of higher education studies have you completed?

Note the use of PPS for the "finished action".

Or, if the candidate is still studying:

How many years have you been studying in higher education?

Naturally, my examples work just as well with a more general "time query" (ie "How long?") if the answer doesn't need to be specific.

I hope that answers your question fairly well. Maybe I went into too much detail on PPS/PPC and confused you (I hope not!). As a final observation, I think your first question reads more naturally without "for".

To your first question:

I have been going on package holidays for years and I have never had any problems.

The Present Perfect Progressive has the meaning of "lately" or "recently." There is no indication from the second phrase that she stopped going on these trips long ago in the past. In fact, it sounds like she still may be taking trips, thus the answer.

The answer to your second question also lies in the second phrase. He is referring to the fact that he was never sick before from the foods he had already tried, not the food he is continuing to try, because obviously the most recent food made him ill.

I have been exploring the world...

The distinction is slight, but perhaps can best be explained as, there is no indication that the subject will stop the activity. The alternative

I have explored the world...

does not hold that implication. It could easily end with

I have explored the world for over 15 years, and it's time for me to settle down.