(No experience on HAL, but have been looking into them.)
That looks so fun.
My initial take is ship’s shore excursions may not matter. But definitely it would for Morocco, Israel, Tunisia (my opinion). Safety. Unless they have not visited a specific port, I would expect them to have some good offerings available. And, yes, private bookings could fill in where ship’s excursions are slim. Viator and TripAdvisor are useful advice (same ownership).
(We visited Tunisia on a
Disney cruise. Took a long drive to Dougga, a UNESCO archaeological site - would recommend if you enjoy this stuff. I have photos…

)
My memory is that average age in HAL is only 6-7 years older than the industry average. But does it even matter - if you are not shopping for a life partner.
I expect most long, unique, sailings to be in older vessels. It comes down to what you think cruising is for you. Nightly entertainment? (My research on HAL is they are heavy into music as entertainment.). I can’t imagine 42 days on any cruise is going to offer a variety of food that wows me. Eventually you can fall into a pattern where you just eat reasonably without having to try everything.
I would definitely check out Cruise Critic for the ports.
Watch some videos to ”see” the ship.
If you are a big fan or Royal or Carnival, I would question this as a choice.
I have mostly sailed Disney. I would probably pick Princess as second choice. Tried Royal, NCL, Carnival, and MSC. Can’t say I regret any cruise I have taken. Been toying with idea of HAL or Celebrity. Can’t afford Viking, but would love to. Every cruise has some aspect that isn’t my favorite (smoke, loud music / party vibe, or food come to mind). But I have a lot of great memories.
My worst cruise memory is actually on Disney - uncomfortable bedding as 2nd guest in Concierge. Good thing it was just 3 nights!