I started running at 40. I went from nothing to now having 5 marathons under my belt. If I had a pound for every time someone told me it was bad for my knees, I'd be rich.
What I've learnt, the hard way, is that strength training is crucial to prevent injury (of any kind). I ran for a few years without doing any other exercise, and over time this caused more and more pain in my calves. It took a while to diagnose, but eventually it was traced to a weakness in my back and glutes. I now do a load of squats/lunges and back strengthening work, and am finally (after over a year of pain on every run) starting to be pain free.
The other thing that's great for injury prevention is to vary the terrain you run on. It's hard at this time of year, but including some off road gives your joints a break, and works the muscles differently.
Build up slowly (C25K is perfect), and there's no reason at all why you shouldn't enjoy running as a way to get fit. If there's a running group near you, they can also be a great source of support and encouragement.
(No qualifications as such, but I am a EA Leader in Running Fitness)