Rail Pass or Point to Point for a 70 year old traveler

Check at the Man in Seat 61 website for lots of useful details about Rail Travel in Europe.

Check with the train operators for your specific travel dates to get fares and times-

Vy Norway for the Bergen to Oslo journey- https://www.vy.no/en

and SJ (Swedish Railways) for the other two legs- https://www.sj.se/en/

You can also book Oslo to Copenhagen with Vy Sweden- https://www.vy.se/en and Vy Norway lets you book through from Bergen to Stockholm if you are just going straight through without a few days in Oslo.

but better with SJ as they are the actual operator

With a railpass you would still need to make compulsory reservations on top of your pass fare.

As mentioned, compare with the price for single tickets at www.vy.no and www.sj.se but I have the feeling that a Eurail pass (if that is what you're looking at) will not save money.

If planning for a trip several months away, you will get the most value—not with a rail pass which will run about $300 for four days of train travel plus reservations costs—but by buying your train tickets in advance when they first go on sale. In Europe, train tickets rise in price the closer it gets to the date of travel— similar to the dynamics of buying airline tickets . For Norway, the Bergen to Oslo tickets can be bought online directly from Vy, Norway’s train company. when they first go on sale 90 days in advance for about US $70. Waiting until a couple weeks before traveling and the same ticket can cost $130. www.Vy.no/en. Is the website to buy your tickets. The Oslo S to Stockholm train ticket can be booked online with the SJ train company. SJ runs high-speed X2000 trains on both the Oslo to Stockholm route and from Stockholm to Copenhagen. You can buy tickets online at www.sj.se/en up to 5.5 months In advance for a little as $30 on each of the two routes. From Stockholm central Station to Copenhagen, a change of trains occurs at Gothenburg.

I like to add that there are also other travel options, e. g. flights and ferries (Oslo - Copenhagen).
Therefore I recommend to consider changing the row of cities and widen the possible ways of transport.

btw: I miss the landside in your posted part of itinerary, especially Fjord Norway except overcrowded Myrdal - Flam option.

Stockholm to Copenhagen does not route via Gothenburg. That is a long way round. The normal and significantly faster routing would be via Malmo, some of which services are through to CPH, no change.

That no-change-of-train is an improvement and cuts travel time to a little over 5 hours!

I think I occasionally got a senior discount on a Norwegian train ticket. Early purchase might have been even cheaper, but I tend not to plan details terribly far in advance. I think in Norway, at least, you can pay a bit extra for tickets that are at least changeable (maybe refundable; I don't remember). That would probably be smart if you're buying way ahead of time.

That no-change-of-train is an improvement and cuts travel time to a
little over 5 hours!

Yes, that was a big improvement in 2000 when the Öresund bridge opened and SJ started running direct trains between Stockholm and Copenhagen. Previously, passengers had to change in Malmö from train to a ferry for the last bit of the trip to Denmark.

I think in Norway, at least, you can pay a bit extra for tickets that
are at least changeable (maybe refundable; I don't remember).

The same is true in Sweden. SJ has three categories of tickets. Non-refundable, rebookable and refundable.