I guess it depends on what you mean by "successful." Do you mean placing in competition? Or accomplishing the goal of "bulking up" to the best of your ability?

I'm not bodybuilding per se, but I began doing resistance training as part of cardiac rehab (last year, at age 47), and I was surprised at how much gain I was getting in a fairly short time. It wasn't much by competitive bodybuilders' standards, I suppose, but within weeks I could see where my arm muscles were where I had never seen muscles. I have always been a rather soft, roundish couch potato, never jocklike by any stretch.

I've learned, now that I've slacked off a bit and been focusing more on cardio, that I was training a bit aggressively without even knowing it (only doing weights a couple or three times a week, but adding weight pretty steadily), and that could be why I saw some gain in a relatively short time.

The moral of the story is that people (like me) who *never* imagined that they could bulk up at all, ever, may actually be constituted in a way that they bulk up with just a bit of steady effort. Other people don't bulk up no matter how they devise their routines or how assiduously they apply themselves to them. You don't know until you try. It's sort of like how you didn't know until you pubed how long your dick would wind up being.

In any event, the worst that's likely to happen to you (provided you don't overtrain) is that you would at least develop a bit of strength and a bit of muscle-tone, even if you don't bulk up considerably. And that couldn't hurt.

The exercise physiologists at the facility where I've been doing my cardiac rehab have been stressing the fact that aerobic exercise, while it may work the same muscles as resistance/anaerobic exercise, doesn't work muscles in the same way. So if you have a swimmer's build because you're actually a swimmer and not just lucky, even if you have well-developed swimming muscles, you still won't necessarily know for sure how your musculature will respond to resistance training.

Again, the moral is that the only way to find out is to try, and if you're in good health, there's probably no reason not to try. But checking with a doctor first is a good idea. (I was 43 when I had my first cardiovascular event, a "silent heart attack." But I had no delusions of ever having been physically fit.)