I have come to realize that there is a 'will to live' to seek activities to enhance that goal. That means that anything the 'elderly' person believes will give him/her the tools to prolong and even make interesting a viable existence.
Walking is still excellent in this regard! do not limit the mind if the goals are positive. I would also that that 'elderly' is a loaded term. TOme it implies people over 70 years but I have seen people at 55 exhibiting the same lack of mobility as those who are able at 70 years. One fellow from a taiji class about 15 years ago
was a freshman in college at the time and when he graduated, he could bared walk due to his reliance of medication for his OA/RA condition.