Go to the link first if want but here me out as to why these are good choices.
Eisenberg is a good actor. (remeber the Scott Pilgram movie). And a young Luthor puts him around the age of Superman. Please remember that, in some comic stories, Superboy was responsible for the loss of his hair. Also the TV show Smallvile.
Irons is a great actor no matter what role he plays. Like Michael Cane, he will bring much to the role of Alfred.
That's my thoughts on this.
Go Forth and Do Well