I'm a climber and finger strength plays a huge role in our sport. If you have the time to pick up a new hobby I would highly recommend going indoor bouldering. It's honestly incredible and you might just get addicted.

If you're just looking for a means to an end, you might want check out hangboarding or grip training via a pinch block, or one of these devices... You can easily find all of those online, however hangboarding without a decent climbing background isn't safe so if you do go down that route you'd want to really do your research and use a very very conservative program. In your case, simple grip device would definitely be safer and simpler than a hangboard.

Hope this helps at least a bit!

​

E1: As for endurance, starting a consistent cardio routine does wonders. Whether it's swimming, cycling, running, even brisk walking it'll all do the trick as long as you spend a couple of hours a week on it.

r/C25K is a great resource to start / restart running.

E2: I wasn't clear enough with my wording originally. Anyone without a decent climbing background or a good level of baseline fitness should not hangboard so I have changed the wording to reflect that. Thanks to u/TILjamming and others for the clarifying comments and proper advice.