Mobility equals freedom. If you don't believe me, live without your car or public transportation for a month.
Same goes for the human body. If you are immobile for long periods of time, IE sitting at your desk for 9 hours a day, you feel decrepit and unwell.
Mobility is getting yourself into positions of power. Running, squatting, pull-ups, snatches and wall balls all require mobility to do correctly. Can you do those things with minimal mobility? Sure, you can train yourself to move in compromised positions, but you won't maximize output through those poor mechanics.
Take 15 minutes a day for some kind of movement practice: work on handstands, mobilize, do yoga, hang from a doorframe. We're not talking about working out again, so running and swimming don't count. 15 minutes a day becomes 90 minutes a week equals 78 hours a year. You'll feel tons better relative to the zero hours a year you spend on it now.
Remember, the folks in the old person's home are there because they can't function. They're immobile. Get out of that chair and move!
200m row or run
10 kettlebell swings
10 back extensions
IT Band, hip flexor