How, again according to Dostoevsky of Notes from Underground, is a man either intelligent or ignorant?

In Part I, the protagonist says that in fact he was never a rude official, but had just lied to the reader out of spite; he instantly goes on to say that though he had tried to be spiteful he could not be because his nature contradicted it. His nature would not allow him to become anything or to have any character at all, since intelligent men cannot have character. Men of character and action, on the other hand, are never intelligent. This is what he believes at the age of forty and must therefore belong to the wisdom of old age; forty is extreme old age since no one should ever live past forty.