I am also pushing fifty and have read a lot, life’s too goddamn short to not give up a book the moment you stop giving any fucks about it.
I read a lot, but have a lot less time for it since I started biking to work instead of taking the train. This is best viewed IMHO as making the best/most efficient use of a scarce resource. If you are really just dragging through a book because you don't enjoy it, or its tedious, just drop it. When I read a truly great book, it sticks with me forever, its a shame that I hadn't read it earlier.
FWIW, Wheel of Time is actually what made me ok with dropping books/series. That series was just an enormous drain of my time, and personally, I thought it was really poorly written and excessively long- I stopped caring for the characters and secretly hoping even my "favorite" characters would die just so we could get on with things. After the end of Book 7 I just said enough is enough, I am accumulating a pile of books I actually want to read and just dragging through these 1000+ page slogfests because of stubbornness about finishing what I started. Tugs Braid Smooths Skirt
If you're not adverse to wearing ear buds while biking (I know some people are, for situational awareness reasons) I recommend using FBReader with the TTS plugin for 'reading' ebooks when you can't have your eyes on the screen. I do this while running. The computer voice is offputing for an hour or two but if you push through that it becomes a great way to get through books using time that would have otherwise been book-free.
There is also the trouble of "A/V sync", wherein you want to mix reading the book with listening to the book. You can do this with some proprietary solutions like Kindle if you purchase both the ebook and get the audio book, but this is again limiting.
Some don't.
The rule of thumb fails.
If someone has reason to know that the book does get better, then great. But it's no reason to grant every book that much leeway.
The whole you have to watch/read/listen to X amount before passing judgment is bullshit. If I surround a chocolate cake in three inches of shit, no one will fault you for not eating through the shit just to get to the cake. It might be a good cake. It might be the best cake. But I'm not chowing through three inches of shit just to get it.
Maybe next time, don't cover your cake in shit and see how that goes.
The point is that if the creator wants their work experienced, they must make the experience enjoyable in some fashion all the way through.