Learn English – I never knew/have never known the grandmother as she died before I was born

I've worked here for two years usually means "I've worked here for two years and I still do". Occasionally it might simply express express the continued relevance of the past to the present, e.g. "I've worked here for two years - but I've just been fired". Without the expression of time, it could similarly express the relevance of a past event: "Have you ever worked here before?" / "I've worked here before, about a decade ago. I'd be grateful if you'd consider giving me a job here again now."

I worked here for two years usually means "I worked here for two years, at some time in the past, and I no longer do". Depending on context, it could also describe a situation where the speaker still works there today - e.g. (1) "I worked here for two years before Bob left - and I've worked here for five more years since then"; or (2) "I worked here for two years in the 1990s, then I left - and now I'm back again".

I've known her for two years means "I've known her for two years, and I still do".

I knew her for two years usually means "I knew her for two years, at some point in the past, and I no longer know her". Depending on context, it could also describe a situation where you still know her - e.g. "I knew her for two years before she got married (and I've known her for a further three years since then)".

Similarly, I've been hungry for two hours usually expresses continued hunger, while I was hungry for two hours describes the duration of past hunger.

I am hungry for two hours would only make sense if you were describing a regular event or consequence, e.g. "I am hungry for two hours every day between 4 and 6 pm!" or "If I skip lunch I find that I am hungry in the afternoons".

It depends on exactly when the speaker is talking. Is the speaker talking about something that happened a long time ago, or did the flight just finish? The simple past in "That was a fun flight" and "It was my first flight" makes it sound like the flight is completely over and done and in the past.

Using the present perfect (have never done) sounds wrong if the flight is long in the past and the speaker is remembering it. The reason is that it is a present tense - it is talking about how things are right now! - and it doesn't make sense for the speaker to say I have never done if he's remembering something something he did. But if the flight just finished, then it sounds natural for the speaker to say "I have (at this very moment) never done that before (this time)."

Using the simple past (did) sounds slightly awkward because the speaker is explicitly comparing two times in the past (because we know the flight is in the past, and because of the word "before") and the simple past just puts an event in the unspecified past. You do hear people speak like this sometimes, though.

If the flight is in the long past, the most fluent phrasing, to this US English speaker, would be "I had never done that before." The reason is because the speaker is remembering a past event (the flight) and saying that before that time, he had never done it. If the flight just finished, "I have never done that before" is OK.