Catchers generally develop slower/later than typical players, so I wouldn't put too much stock in his age relative to his league. He's not a lost cause by any means, but I don't think next year is the time to be looking for him to be a back-up at the big league level. 2023 though...that's the deadline for him.
It's usually the bat that develops later though, isn't it? Bad defensive catchers tend to stay bad defensive catchers, at least after a certain age. Most players start to decline defensively in their mid 20s, I'm not sure how catcher defense trends. Sometimes, when they start to hit a lot in the minors, their defense gets "talked up" like Ryan Lavarnway, but they are still terrible catchers.
edit: Ronaldo is better than Lavarnway. As Sox prospects notes, a lot of Ronaldo's faults would go away with a robot ump.