It's probably a stretch scientifically to say dancing reduces the symptoms of aging. It would be more accurate to say that physical exercise that requires the coordination of multiple forms of physical stimuli simultaneously is more effective than those forms of exercise that coordinate less forms of stimuli. Dancing is just one beneficial coordination form of exercise and it is rather limited in the number of muscle groups that it works, but if people consider it a source of amusement and fun - that in itself is an advantage, because they are more apt to engage in it and more frequently.
Limited number of muscle groups? Try Lindy Hop. :)
"Elderly volunteers, with an average age of 68..." 68 is NOT "elderly."
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Lofi version of phys.org