Mountain Sitting Immortal - Chapter 12: Crazy Dog Killer.

... n't be ready by 13 years old, while children with good food and who were given regular medicinal baths to strengthen their bodies are likely to become ready by 10 or even 9 years old.

He has had some medicinal baths ever since he was born, but they were once every month, not every day. He also didn't eat any special treasure or meat, so it is an anomaly that his body was ready for training right from when he was five years old.

It is still an anomaly that he is ready for training ...