While listening to NPR yesterday I heard the reporter refer to an active centenarian as "spry." This term seems to be commonly used to refer to active older people, yet we (in the USA, at least) refer to active young people as simply "active." Why? And why, for that matter do we call older people "Senior Citizens?" They may be citizens of Guatemala or Greece, for all the speaker knows, so the term seems silly to me. How is it in the rest of the world?