This is just SUCH an interesting thread and I think we should all be proud of ourselves!
I'm 47 also (can't believe how many of us there are!) and I've just noticed, really in the last year or so, that I need to take it down maybe a "hair of a notch," but really I feel stronger and fitter than I did when I was in my mid to late 20's (when I first started working out) and all through my 30's and even early 40's! My joints are a little achier than they used to be, with maybe a little more frequency, and that's why I've taken it down ever so slightly in intensity, which is hard for me to do since (like so many of us here) I'm sort of an intensity freak! But I have to admit I'm enjoying incorporating more stretching/pilates/yoga-type stuff...it just really feels good! 