There is no skill limit for Rookgaard and Downport. On Rookgaard, there’s no level cap, so you can continue killing monsters and training your skills as long as you want, meaning there's no limit there.
On Downport, you can train with a monster called the Salamander Trainer, which has a lot of health and heals itself — even healing up to four people at once — while doing very little damage. This allows you to train without killing the monster or gaining experience. If you eventually reach a skill level where you're able to deal enough damage to lower its health below the healing threshold (once it’s in the red), you can then focus on the summon, which also doesn't provide any experience.
If you want to train magic levels while skilling, you can kill deer, sheep, and rabbits since they give no experience. You can then sell the meat and use the proceeds to buy eggs, which are the most efficient food for regeneration/oz. So, to sum it up, no, there is no limit.
