I think most elderly people just don't remember their dreams most of the time. As far as i know the dream related abilites get weaker as you get older...

It's basically true for most adults as well... most people are too busy to care about their dreams, so they don't even remember them.

I told my mom about lucid dreaming when i started (2 years ago), but she is too busy all the time because of work, then the things that need to be done at home... so she never remembers her dreams.