This, 100%. My dog is like clockwork. Start with a really, really frequent "out" schedule and then you can slowly decrease the number of trips over time, as your dog gains control.I'm not a fan of bell-training. I've bell-trained two dogs and both learned to ring the bell whenever they wanted attention of any sort. (Probably a flaw in the training, but I'd rather poke myself in the eye with a sharp stick than have another bell-trained dog in the house.)
An alternative is to take you dog outside at regular intervals. Dogs who are on a consistent feeding schedule are remarkably regular. I think it's a lot easier to learn a dogs schedule and follow it than to have the dog bark, scratch at the door, do a little dance or ring a bell when she has to go out.
If you insist on doing it, it's certainly not too late. I've taught a 9-year-old dog much more complex behavior and I'm not a good trainer. In fact, a dog much younger than yours probably doesn't have the bodily control to advise you when it's time to go outside.