If the son just graduated college, looking to get married and has a decent job, this is the best course of action IMO.
To me, there is a difference between building and subdividing on your land for an older parent for you to help keep track of and help take care of, but building and subdividing land for a child entering marriage, new career along with new possible family opens up a host of other possible future complications on something that was once your land.
Possible scenario... everything right now is honky dory. 2024 you give them a piece of land, they build on it and they're "next door"( 2 years from now). Lots can change in two years. Son finds out the girl is bat ***** crazy AND she has family that wants to live there as well. Son gets tired of the crap, moves out, and your stuck with a bat ***** family. Yes, I went extreme per my example, but never say never, particularly with younger "kids".
Sounds like the OP did a great job in raising his boy. I'm thinking with a decent job and a new wife, he should be able to figure things out for the next 5-10 years on his own.