Met a guy this week while I had my cycling clothes on so he asked me if they made a bike for someone his size. He was 5'8" and 420lbs and probably in his late 30's. When he was not walking, he had to lean on something to help his balance.
I told him that it might be possible if he got a strong frame and wheels with a very high spoke count but I was not sure what to recommend. I told him that a recumbent trike might be a good bet but later I realized that he would probably be unable to get out of the seat without help.
Are there any clydes here that can relate to his situation? What kind of bike were you able to ride? I would like to pass the info along to him if I see him again.