The glaring problem with the measured benefit here is that walking ability is a great determinant of overall health. Any senior able to walk 3k is already well

The glaring problem with the measured benefit here is that walking ability is a great determinant of overall health. Any senior able to walk 3k is already well above the others in health outcomes, and less likely to die than the rest, regardless if they walk 3k everyday or not. It's like claiming driving a Ferrari will make you wealthy, because you observed that Ferrari owners paid off the biggest speeding tickets. Then advising people to buy a Ferrari to be wealthy.