The "old person shuffle" can involve a multitude of issues. One of my old teachers from Taiwan would say that the Rape of Nanjing happened because people couldn't stretch their legs to run away. He complained that the Chinese people then were not physically fit. That didn't include martial artists. But, at any rate, it's what eventually led to the mass physical education programs. Still, we can see elderly Chinese people shuffling.
There are loads of studies on gait. Fwiw, I had to almost completely relearn how to walk after a spinal operation. When they say, "All it takes is putting one foot in front of the other," they're lying
. One thing that you can always observe is stride length. Shuffling means taking small steps (for any number of reasons, including balance). A longer stride (if you are lucky enough to be able to stride), indicates a more efficient system. Arm-swing also plays a part. Older people who shuffle do not swing their arms. However, that swing is affected by shoulder, waist, and hip mobility (or spine, generally). If your back is stiff, etc., etc.
Also, because balance is involved (as Klonk importantly points out), eye, ear, and head position is important. If you look down, you throw off the ear orientation. Moreover, now your head wants to pull you forward. So, your body weight goes to the front of your feet, and you are essentially falling into each step. That can lead to hammer toes, but the effect is to slow the gait down to avoid pain in the feet. Slowing down also means that there is a tendency to do less walking, and you can imagine where that leads.
That's my experience.
"A man is rich when he has time and freewill. How he chooses to invest both will determine the return on his investment."