Give me the Death Note, I can be trusted to act rationally. The only “undeserving” to end up on it would be people who step through Metro doors and immediately stop, even though there’s people behind them.
More seriously I know the author has said it’s about power corrupting, but if that’s the story he wanted to tell then he should’ve chosen a different protagonist. Its also a silly mantra, we do not live in a Tolkien novel, power isn’t some supernatural force.
After your first go, you just need to wait 39 days and your Shinigami appears, and you can ask them questions which they have to answer to the best of their ability (which isn’t guaranteed to give you the full detail, as they might not know it). That should give you a good opportunity to workshop exactly how to phrase dies of some disease that can’t happen until they’re old so the auto-selected date is some point where they’re already old, but if they were already going to die before that, dying at their predestined time of an accident or disease is fine, too and make it work.
I did see that there’s another tab to the article that phrases the 23-day rule differently, stopping you set death times further in the future than that, but then immediately explains how death times after that work for diseases, so that’s obviously self-contradictory.