If you are an old lady, remaining spry is something you aspire to. It means "nimble." You might also use it to describe a goat that jumps easily along from mountain crag to mountain crag.
The most common use of spry is to describe people who are aging. You might say that at 92, your great grandmother is still spry and sharp as a tack. Spry refers to her physical well-being; "sharp as a tack" to her mental faculties.