The surgery went fine and the rehab was long and arduous. His surgery was in Oct of 2017 and it was a full year at least to start to get back to where he was. There is no way he could have played in 2018. Maybe, and I say maybe he could have come back in 2019. Being an athlete he worked hard at rehab, and once released continued to work at it (rehabbing exercises) while he worked out. He made the decision to retire after the surgery, he was 25, in love and ready to start a life outside of baseball. I don't know if he could have continued to play, he's still getting calls from high level independent league teams checking to see if he'd like to play again but he's comfortable in his decision. The one thing that he said really hasn't come back is over head strength, like putting up a ladder or chopping wood.
So where is he now? He's 27, engaged, he's working in a management program for a fortune 500 company, he has a dog and can actually go to the beach or out with friends, something he hadn't been able to do since he was 9. He still loves baseball and doesn't regret for a minute all he gave it or all it has given to him. He's in his second year coaching youth travel teams for a large national championship level organization.
Advice, follow the doctors orders, take a red shirt year, be patient. When he does start playing again be aware he will not be at the level he is now, it might take a year or two to get it back. Work on his grades, prepare for life after baseball.
I wish your son the best. He's got youth on his side, he can afford to miss a year or two and still have a great career in baseball. Just don't hurry him back. If you want I can put him or you in touch with my son and he can discuss his experiences with the surgery and rehab.