A few thoughts:
1) 55 is a pretty slow 400 for a 2:03 800 PR, and probably indicates that our 800/1600 guy should really think about being a 1600/3200 guy
2) I went my entire high school career without getting a single injury, but had many issues with injuries in college. Just because you are injury free now doesn't mean you should be foolish about your training or neglect injury prevention
3) His training plan really depends what time of year it is. In the winter, He should build up to 60-65 miles per week with perhaps one high-end aerobic workout per week and, if his heart is really set on mid-distance running, one light speed session like 12-16x200m at mile pace. Nothing crazy.
Long term, the goal would be to move up to the 70-80 mile range if the focus is the mile, but it doesn't make sense to jump right up to that from fifty miles per week even if you think you are "impervious" to injury.