I wouldn't put much stock into that statement if he really said that. If that were true, DC would've ended around 1000 chapters, and we're currently at 1021. It's similar to the One Piece editors/Oda saying the story is like 60-70% done every few years in an article. Now that Gosho goes at a pace that likely won't lead to a burn out, DC should continue for quite some time. There's still a lot more we need to know, and we've been getting some progress as of late. Maybe like 5-7 more years? not really sure.