'Fit' is a word that describes the muscular appearance and health of the body. A 'fit' person is a person who is 'in good shape' or is physically appealing with their body tone. A 'fit' person has an athletic body appearance. So the question is asking "How physically developed are the bodies of your generation compared to other generations?"

fit = healthy; in shape

In that case it probably means "physically fit", athletic, strong, with attractive bodies, or high energy.