You didn't include the most important factor - what is his training history? A PR doesn't tell his background. I don't think the plan is perfect but it doesn't look unreasonable either if he's someone that has regularly trained 50+ mpw.
Right now my athletes are expected to run 4-6 days a week based on their individual training history and they will add a day to that when July hits. Younger kids will add another run per week in August, so by August everyone is running 6-7 days a week (and we will maintain that through XC season). I don't schedule down weeks, but when kids have summer trips and other big life commitments, we back their running off and use that time as a down week.
Most of our athletes will run from Aug-Nov without a planned day off. It's fine as long as a few things are considered:
-Don't increase volume and intensity at the same time. If kids are adding a day of running or increasing a long run, drop or shorten a workout that week.
-Build in recovery days. Recovery days in our program don't mean a day off, but a 3-4 mile run (we let our varsity kids slow down and run with a JV friend on these days). For someone that is used to 5-7 mile days, this keeps them in a routine while still giving their body time to recover.
- When workout intensity is high or our races start, our easy runs are SLOW. My sub 18 5k girls rarely run sub 8 on easy runs.
-Take care of the little things. Get enough sleep, eat right, and do injury prevention work.
-Don't be a slave to the plan. We don't take days off just to take days off, but we don't track running streaks either. I have no problem sending a kid home or telling them to skip a weekend run if fatigue is catching up to them.