Most engines never get up to propoer operating temp before they are shut off. Another factor is engine wear. The more worn the rings, the more blow-by and the more contaminants in the oil. So, an older engine propably needs more frequint oil changes.

As a point of reference, when I bought my boat it had a Perkins 4-108 with only 1600 hours on it. Even at that young age the oil turned black immediately after changing. After 5600 hours it was replaced with a Beta BV2203. Now ten years and 3000+ hours later the oil still looks good when changed at 150 hours. My conclusion: the Perkins was abused early in it's life and that shortened it's life.