Bodybuilding (done properly) is about as close to perfect for maintaining a functioning body into old age as you can design an activity: It's easily scalable from zero to infinity, has regression and progression to your abilities built in, and huge benefits from even the smallest investment. It can be performed with basically no impact. It improves joint health. It helps you train to perform every day activities. It can easily be modified to cope with injuries, missing limbs, whatever limitation you have. It benefits you hormonally in a massive way. etc etc
I'm 36. I do about 14 hours of tennis/surf every week, plus maybe 2 hours of gym work and lots of moving around during the day for my construction work. I love my sports but my body would be a wreck if it weren't for the resistance exercise I do to prepare/rehabilitate it. I would do a lot more of it if I were smart.
My dad was an elite athlete who ran for the national team. By age 50, many of his cartilages were worn out and he experienced extreme pain while doing daily chores.
He says you should only jog on grass or sand.
But the same dynamic exists in other sports, including weightlifting. Plenty of causal weight lifters focus on the weight they are pushing exclusively and never consider their bodyfat, go on "dirty bulks" or permanently injure themselves with poor form or pushing it too far (also see CrossFit).
For most people, having a couple of different and reasonably different physical activities, and sticking to them, is going to be enough. The most important thing is that people actually use their bodies into old age. Exercise isn't the rocket science people make it out to be.