People always think pros would shoot a 55 or whatever on their local course, but that's not how golf works. Easy for them to go out and shoot low 60s on a course like that, but breaking 60, even on a short course, is really hard.
Give them birdies on all four par 5s. Sure.
Give them one birdie on a par 3. Why just one? Because even if the par 3's only average 150 yds, the average proximity for the best on Tour will be about 20 feet. And the best on Tour from 15-25 feet is making 1/4 putts.
So now they're -5, and we have 10 par 4s to account for. Let's even say half of them are driveable. Eagle is still highly unlikely, but I'll be generous and four birdies on five holes. So now that's -9, which is a 63 if they par the other five par 4s. Even if we give them two birdies on those, which again, means either hitting approaches inside 10 feet or making putts they statistically shouldn't make, that puts him at a 61. And that's with them playing well and without any silly bogeys.