I'm not trying to be insensitive, I'm just not sure what the specific term is for people who are unable to walk due to physical disability, but obviously I mean these people in particular.
How did people get around without the use of their legs in a time before wheelchairs? Did they at all? What would life have been like for them?
So it depends on a lot of things. Most people that were born with a physical disability like CP or spina bifida often didn't live past infancy/childhood. So their families would often carry them around until they passed away.
Most people who suffered an injury later in life didn't survive the initial injury therefore there was no need. Here is one of my previous comments on the subject: http://www.reddit.com/r/AskHistorians/comments/20l8dv/my_mother_told_me_a_story_about_my_grandfather/cg4j6ju
The reality is as soon as wheels were invented there were chairs. There is proof dating back as far as 5BC of a wheelchair.
As for the elderly, it would be rare to live into your 60s let alone later, and if you did as soon at you lost your ability to self care you would be bed bound and then die quite rapidly.
Edit currently on mobile but I'll answer any other questions!