I have bows from 43 pounds to 72 pounds. I am almost exactly your height and only a few pounds lighter. I am 56 years old, have had past shoulder injuries on both sides, had surgery on my right shoulder (I am right-handed) in December 2005, and even went through an almost life ending bout with stage 4 cancer a couple of years ago. So, I doubt my overall condition is as good as yours. A year ago I could barely draw a 45 pound bow. Now that weight is very easy for me to shoot, and I regularly shoot bows in the 50 to 60 pound range without problems. Like everyone else, I cannot shoot as many arrows in a session with the heavier weight bows as I can with the lighter weight bows, but up to the low 60's I can shoot almost as well. My form starts suffering noticeably when shooting bows above the low 60's. Mostly I shoot in the mid-50's with no problem at all.
Obviously, like all other archers, a 45 pound bow is easier to shoot than a 55 pound bow for me too, but the performance of the 55 pound bow in the same model of bow is much better, and the arrows hit with much more authority. Because some states require at least a 50 pound bow for elk, I don't see any reason to buy an "elk hunting bow" at less than 50 pounds, even if you might go to a state without that requirement.
If you get into a regular (almost daily) exercise program and build up slowly, even someone in my situation can easily get to the point that 50+ pounds is not difficult to shoot. It should be no problem for someone your size and in your condition. Even four months after cancer treatment I had trouble lifting 10 pounds. It took me more than a year of physical therapy before I could start thinking about shooting a bow again. At that point, in addition to working out with my physical therapist, I started using a BowFit exerciser every day to build up my strength and then started adding in the shooting of a 45 pound bow. At first I could barely draw the 45 pound bow to full draw and could not hold at all. I could only draw a 50 pound bow back to about 25 inches of my 29 1/2" draw length. Now, a year after starting shooting again, I can shoot my 70 pound bows for a short time and can shoot 55 pound bows for hours at a time. I shoot my 45 to 50 pound bows a lot for fun and form and can shoot hundreds of arrows from them without my form beginning to suffer much.
If all you intend to shoot is animals under 200 pounds, then a 45 pound bow is plenty, but a 600 pound elk is a totally different animal. A 45 pound bow at close range will definitely kill a big elk if shot broadside through the ribs, but quartering shots require more penetration and 45 pounds may not be enough to make a quick, clean kill. I will be hunting cape buffalo this June/July and my professional hunter is concerned that a 70 pound bow is too light. He is a trad bowhunter himself, so he understands what it takes. I can't shoot a heavier bow anyway, so I guess it will work or he will have to shoot the buffalo with a .470 Nitro Express following my failure.
A 30 pound bow with the right arrows and broadhead and with perfect shot placement can kill elk under many circumstances, just like a .22 long rifle cartridge can. In Africa they do culling operations on impala at night with .22 rimfire rifles and silencers and kill hundreds of impala in a single night, but no professional hunter would ever suggest that his client use a .22 rimfire to hunt impala or other similar sized game. Often people discuss the minimum weapon needed to kill animals; however, just like any other life and death endeavor, there should always be a significant overkill factor built in for the times when less than idea circumstances exist. Shooting at least a 50 pound bow on elk, especially if you are fortunate enough to encounter a 600+ pound bull rather than a 300 pound cow, seems to be a very good idea.
I obviously shoot lower poundage bows, but not often anymore. Onehair is right in saying that after dropping to a lower weight it will eventually begin to feel as heavy as the higher weight. I'm not disagreeing with anyone who says that you should not overbow yourself or that a 45 pound bow is adequate for deer, turkey or smaller hogs. Also, a 45 pound bow will always be easier to shoot than a 50 pound bow. If I were in your shoes I would get a very smooth drawing, fast 50 pound bow and do your regular exercises and shooting so you can shoot it easily. If you are working out with a BowFit exerciser and using it to draw and hold the equivalent of 55 to 60 pounds in an exercise mode, a 50 pound bow will feel as light as a 45 pound bow feels to you now.
One final note. I keep at least one bow strung all the time and have it sitting in my living room where I have to pass by it regularly. I pick it up almost every time I walk by it and draw and hold full weight until I begin to get the shakes. Then I put it down until I go past it again. If you are very stable in your exercises and don't strain to draw or hold the bow, you won't hurt yourself, but you will build up your strength and your ability to shoot a heavier bow very quickly -- certainly within a few months.
Sorry to be so lengthy here. It's just that I am your size and have been through the struggle of coming from near death, with no strength and previous shoulder surgery, to being able to easily shoot bows above 50 pounds. I just don't see any reason why you could not shoot 50 pounds with no problem and have a bow that would legally handle all the hunting you stated you wanted to do.
Allan