It's been what? 3 chapters in 3 months?
Assume that we are 2/3rds of the way through the storyline. I think that's generous, but it is possible we're further than that.
So so that means there is roughly 150 chapters left. That's 14 years or so. Maybe less if we're closer than 150, or they speed things up. However, I'd guess that we are more like halfway through the storyline, so another 30 years isn't unreasonable.