The elderly are deliberately targeted, both by junk mail and by door-to-door salesmen. That's why I've registered my Dad's address with the Mailing Preference Service and his phone number with the Telephone Preference Service - both are free and very worthwhile.
He often used to give far too much information over the phone e.g. "I'm disabled and living on my own...." It horrified me so now he's been told not to tell anyone anything and it's printed out for him to see next to his phone - 'Don't talk to people you don't know!'.
He doesn't answer the door; anyone who needs to see him either has a key or the code to his keysafe - got to keep the old folks safe somehow.