It varies. One grandmother is 96, and only in the last couple of years has she had what I'd call any serious reduction in quality of life. Before that she lived on her own capably and happily. At 88 she was still doing great.
On the other side, my grandparents are 88 and 92. They played tennis well into their 70's, and at least as of 5 years ago neither of them took any prescription medication, not sure about now.
They may yet have some undignified years ahead of them, but all of that is happening *after* age 88. Setting the bar at 68 is seriously low.