Alright before the internet explodes with anger over why Jesse Eisenberg is "Too Young" or "Too Innocent" to play Lex Luthor, let's look at his body of work before comparing the two.
Jesse Eisenberg is known for performances in, the Social Network, Adventureland, Now You See Me, and Zombieland, all of which are films in which he's featured as a young man. This is due to his young features, bright eyes, and lack of facial hair(I mean with the picture above, I can see why he shaves it), for in Hollywood, if you don't look too old, they'll put you in younger roles for as long as they can.
One constant in all of these films is that Jesse's intelligence is always present, and prominent. While I think he would have been greater as the Riddler, we cannot overlook this intelligence in the character of Lex Luther. His casting tells us a lot about the character as well. This Lex is going to be the hyper-intelligent, strategic, business mogul turned politician(eventually) and, with Eisenberg's light frame, we may even see him get into the suit! (ignore my horrible photoshopping job below, yes I used paint, yes I suck)
Another feature, which is not so prominent in his films, but noticeable if you look back, is a potential for maniacal thought. It cannot only be me, but something about him, the way he carries himself, the way he observes those around him, I've always felt he's had potential for evil. This alongside a quirky charm such as that you see in Adventureland can give him the "Peoples Lex" that gets him elected, and keeps him under the radar as a villain, which is exactly how Lex is supposed to be.
I'm not saying Eisenberg is the greatest thing to happen to Lex, and I acknowledge there are many other greater actors for the role, such as Cranston, Washington, etc. What I am saying is we should be excited the fact that Eisenberg is Luther, for now we not only know who will play Superman's #1 baddy, but what kind of relationship they'll have (rivalry, even in age), what kind of character he'll be (supergenius, unexpected), and we get to think about how his age Juxtaposes with Batman's Older, experienced character. Also I feel the age is good for it makes Lex seem new to his life in higher society, which makes sense, for if he had been there long, Bruce would have met him at sometime, and being as careful as my boy Bats is, he would have known something was off with this guy years ago. And as for hair, anyone can shave their head, I mean come on, if that's your major deterrent, something's wrong.
Anyway, that's my two cents, I hope you'll be respectful and acknowledge there's nothing we can do to change it, so we might as well see to good to come. Please share your thoughts, I'm interested in how you all feel as well.