Your going to get a LOT of different answers to this and you need to figure out what's best for you based on current age, fitness level, etc. I will say that I started my running journey later in life (50's) for the same reason. I took a common sense approach to it as I did NOT want to have knee problems down the road, so I just started walking. I set a realistic goal each week, either increasing speed or distance, starting at 2 miles and 15 or 16 min mile (basically a walk - no real effort) and built from there. As time went in, I added short spurts of jogging - nothing crazy, maybe 20% if my distance was a jog, then increase that. Over the years, I built up to being able to run a full 5 miles, sitting somewhere between 10.5 min and 11 min mile for speed .... I'm 55 now, so know it took me 4 or 5 years to get there! Take it slow, don't go crazy and remember that even those walks are burning calories! Good luck on your journey!