The Downton Abbey star, 77, is convinced film fans over a certain age feel alienated because so many new movies are aimed at young people, but she hopes the public's changing tastes will soon be reflected in cinema listings.
Smith tells Britain's Daily Telegraph newspaper, "A lot of grown-ups would like films for grown-ups and about grown-ups. It seems there is a change in what audiences want to see. I can only hope that's correct, because there's an awful lot of people of my age around now and we outnumber the others.
"I think of films like Cocoon and Driving Miss Daisy and they always seem to be fairly successful, so it's a bit baffling as to why everybody has to be treated as if they were five years old."
Smith was last seen on the big screen in The Best Exotic Marigold Hotel, which featured an older cast of actors including Dame Judi Dench, Celia Imrie, and Bill Nighy, and her new film, Quartet, stars Tom Courtenay and Pauline Collins, who are both in their 70s.