Do you think that young, beautiful people make less convincing actors than older or plainer people?

I find young, beautiful, well made up actors and actresses with perfect skin and features (eg. Natalie Portman, Scarlett Johannson) generally less convincing in their parts compared to the likes of Cate Blanchett, Philip Seymour Hoffman, James Gandolfini, and Helen Mirren. Do others agree?