I think this is just a rather blunt tool to encourage people to be more active . Not all steps are the same. Walking on level flat ground, going up stairs, walking up hills on uneven ground, walking down paths on gravel, walking as quickly as you can, walking slowly to take in a view or let the dog pee all do different things to our bodies and variety, change and challenge are all relevant too. Just getting off our backsides and moving is so much better than just sitting and if you can add in some strength work that is even better. One of the weights classes I go to has participants from women in their 30's to 70's. I'm the oldest at 77 and we have all shown improvement. We are stronger and hopefully we will have improved our bone density and flexibility too, it's also good fun. Another that I do weekly is outdoors using an outdoor gym provided by the local council, again all ages and a couple of men too. Exercising outdoors is really enjoyable even in January even if we get a bit wet! Nothing a change of clothes and a hot coffee doesn't put right! IMO it's never too late to get a bit fitter.