Mental Retardation is a phenomenon in which special care/ education is the best treatment to enhance the skills and the capabilities of the patient. And since the attendants come to know about retardation by the age of 3-5 years, the intervention of therapy should be commenced then only or at the earliest possible. At the age of 28, the best you can do is to engage him with a special educator, psychologist and a vocational trainer. The team would assess the capabilities, isolate the problem areas and prepare him with some skill that will keep him occupied in a therapeutic manner. For the problems you are facing for past few months, the patient might need behaviour therapy, which can be taken care of by the psychologist. Since above-mentioned treatment plan is time consuming, it should be planned in the same city where the patient is staying.