The last few years in my training, I've stopped jogging, running, and jumping (box jumps, jump rope, etc). I'm 53. Those high impact exercises are hard on my knees. They're great for the leg muscles and the lungs, but just hard on the joints. In place of running, I use an AirDyne bike. I like to stand up on it rather than sitting. It's a great substitute for running and jogging, and it involves almost zero pounding on the knees and other joints. Just as good for muscles and lungs without the joint pain. The rowing machine is also great for cardio and is low impact.
Along with that, I do a lot of single leg strength work with weights - Bulgarian split squat, step ups, lunges, etc... Still do heavy and deep squats too. I find that stopping at parallel puts more strain on my knees than going deep. Everybody is built differently. For exercises like squats, I don't think there's one single form that we should all use. Find the form that works best for you and is most natural, and go with that. Just don't skip leg day.
For me, it's all about being fit AND injury-free. I will never be 25 again, so I don't try to be. All that would get me is injuries, aches and pains that would slow me down. But I'm in better shape than all my friends who are my age (and most who are 10 years younger than me), so I call that good.
I just wish there was some way to simulate altitude in my training program down here at 1,800'. No way to do that though.