A broken rib can be very, very painful, and should definitely be checked out a physician. Hopefully your son is improving day by day and recovering from whatever injury
or accident led to the broken rib. A patient's recovery from this kind of injury is very dependent on the context in which the fracture
occurred. For a young patient, unless there are other underlying health problems, a rib fracture generally requires a significant amount of force, so he may well have underlying bruising or muscle and/or soft tissue pain from the injury.
Strictly with regard to the rib itself, the new bone should be formed in 4-6 weeks. He will probably be sore with deep breathing for that time, and the area may also be sore to palpation for much of that time (although hopefully improving significantly week by week). The biggest change for a young and potentially active adult is getting used to some restrictions on activity. It may be painful to participate in vigorous exercise in the first week or so after this kind of injury. However, the good news is that rib fractures usually heal without any problems.
However, since the details of your son's cause of fracture and expected recovery are unique to his health situation, any questions about his recovery and prognosis are best answered by his primary care physician
who knows his history and can perform any needed exams.