I think you're asking about referring to all elderly people as a group, am I right? I would use the phrase "the elderly" and you would use a plural verb, e.g. "The elderly are at greater risk from the flu."
Be careful, though. "The elderly" isn't always politically correct. I often see people write "Older ________." E.g. "Older Americans/New Yorkers/people/etc. are ...". You would still use a plural verb. Hope that helped!