Here's a response from a little different perspective--that of an old fart. Yeah, I'm old, a little on the south side of 70, and I've learned a few things. Bottom line--it's all about health. I've been pumping iron since my teens, but even that was subject to phases. For example, did the (non-competitive) body building bit for a while, until the needle set became so pervasive (wasn't my thing, so lost some degree of interest but still dabbled with free weights). By middle age (40-50?) it became obvious that just staying healthy and in good shape took more effort and dedication, but the overall rewards were still just as sweet. To age may be an inevitable process (if one is lucky) but it need not be debilitating--that is largely up to you. If you don't find living a long and healthy life sufficient motivation to do something about it (every day) than you may have far more serious problems that may merit immediate attention.
Humans are subject to trauma and disease, stuff you can't always avoid; but the healthier you are when such slings and arrows of outrageous fortune cross your path, the better your chances of survival.
Here's the crux of the matter: your lifestyle will dictate your health and quality of life. Diet and exercise are integral. People are individuals, so no one program works for everybody. Find what works for you, stick to it, and modify/customize it as deemed necessary. The key is Do Something Every Day. Start small if necessary, but do something for yourself every day. No one else can do it for you--your health is your responsibility.
My routine has simplified over the years; having a room at home designated as my gym helps. In a typical week I'll hit free weights every other day (modest weights, more focus on reps & form); on off days I'll do push-ups (510 in sets of 20, 30, 40, 50, 60, 70, 80, 60, 50, & 50). I'll usually take one day out of seven as a rest day. Yeah, I know the whole routine doesn't sound like much, but it works for me. And I gotta admit it was nice to hear my primary care physician comment when I went for my usual annual physical after qualifying for Medicare at 65 (now called a wellness visit . . . go figure), "You're in excellent condition for your age." I kinda winced at the "...for your age" part, but I've come to realize that's one of the nicest things you can hear at any age.
Now get up, do something, and live your life.