Walk into any conversation about "healthy ageing" in India today, and you'll hear a familiar checklist: eat clean, walk daily, sleep well, get your numbers checked. It's a good list, but it's missing something fairly fundamental. None of it works particularly well if your joints won't let you move freely in the first place. LightYears Health, an MIT-incubated nutraceutical company, is trying to put mobility back on that list, starting with the joint most people never think to plan for: the knee.