Thanks Chris and Garrett.(^_^) I see it. Your both fabulous answer help me a lot. For Garrett, I means the older not the "LaoWai".

你要说“老外”吗？"The elderly gentleman/lady" 即可。the elderly foreign man/woman 也可以。可是老外不一定是真的在说那个人很老。。。你也可以形容你指的“老外”。比如说"the elderly man/woman with the white hat on" 。

Neither of those are right. Often we refer to older people as "elderly" or sometimes just say "retired" if is appropriate. There is no specific way of saying someone is both older and foreign, so you have to write out the whole sentence, for example: Elderly French people enjoy cheese. You could technically say, "Elderly foreigners enjoy cheese," but that is a very vague and general statement.