That is where exceptions come into play. Yes people with disabilities (which could include elderly people) will need a different form of transportation.

But exceptions to allow those that need it to drive or other services (like grocery delivery) can take care of that while still allowing for a pedestrian focused city.

There is also the fact that if a city is properly designed ideally you may only need to walk a couple blocks for groceries and your basic needs, and instead of doing big shopping you buy just a few things at a time.