Since I've already humiliated myself on this site by confessing my weight, lol, I guess I can't do any more damage by replying. I'm nearly 60 years old and weighed 285 when I started bicycling back in July of this year. In my ignorance about bikes, I had no idea that that would be an issue, and just bought the prettiest cruiser I could find, since I hadn't been on a bike since my single-speed when I was 12 and had no idea how derailleurs worked! I bought an Electra Hawaii 3-speed beach cruiser with a steel frame and fork, and started riding.
I ride on paved streets/bike paths nearly every day. I'm up to 7.5 miles a day now, and increasing by 1-2 miles a week. It's fairly flat terrain, so I don't know if anything would change were I going up and down hills, but so far my bike shows NO signs of problems with my weight, other than the spring beneath the seat squeaks occasionally (in protest, I imagine, lol). I've never even had a flat, which was the one thing I did worry about due to my weight, but stuck with the tires that came with the bike.
Tell your friend that according to my bariatric physician (the kind that specializes in weight problems), bicycling is the greatest exercise an overweight person can do, because it's easy on the joints, unlike walking, tennis, football, etc., and you don't have to be a speed demon to do a lot of good. I've lost 30 pounds by biking and eating healthy foods to fuel the energy needed, and continue to lose weight. More than that, I feel so much better on the days I bike, after I've recovered from the exertion, that I really MISS the riding on days when I can't -- like today, when it rained all day.
Tell him for me that the first day I rode, I went about 1/2 mile, VERY slowly, and thought I would die -- went home and had to lie down, lol. But I stuck with it, going just a little further each day, and now I do my 7 miles now at 12-14 mph, and it doesn't seem that hard at all, so I'm working at increasing both distance and intensity. Cycling has given me the confidence that I can finally GET this weight off, once and for all, doing something that's actually FUN and doesn't hurt. I hope it helps him do the same.
I wish him luck.