My mother is in her late 70s and I didn't let that stop me from waking her up. Of course, upon my immediate family leaving the Borg, she had to know why (rather than just shun us, bless her). So I told her and showed her why. She's fully on board with our decision and hardly ever goes to a meeting anymore herself. She doesn't have the friendship infrastructure in place to completely DA but she's mentally free and we're all the happier for it.
Is it difficult for her at times? Sure. But I don't think you're doing anyone any favors by leaving them hostage to a mind control cult, no matter their age.
Faithful older JWs are in constant fear that since they can't pioneer or make all the meetings anymore that they will be destroyed by their loving God at Armageddon. I think letting them finish out their life in uncertainty is a LOT better than finishing it out in fear.