Don't spook him! Let that common ground be something he can feel good about and make yourself very approachable to him so that he can call or write you and tell you things. He isn't going to know that much of things when he first gets there, but he will have some stories-and so do you. Think of it as he is a hill on the coast of CA. They naturally wear away gradually, but when do folks notice? Then you get a big storm and sheets of coastline fall away into the Pacific.
He is going to see some 'rain'. You can drop a little of your own. Eventually there will be a ****storm at Bethel for some reason or another and it might get him out. Ask about a bunch of names that are no longer there (if you know they were kicked tothe curb after decades, all the better). Ask if some obnoxious meal custom still goes on (any funny stories?). Remember some of the things that affected/disturbed you at that age and ask if they are still like that. Ask him how he feels about the drinking or whatever goes on that is dodgy for a bunch of monks and nuns to be engaging in. Get a feeling for how he feels about the place. Don't scare him from knowing he can talk freely to you. You can be positive about things (nice getting your laundry done, eh? You think those college boys have houskeeping, laundry and meal prep for them????)
Poor kid:(