Give Reid's archetype, its pretty easy to see why you either get confident!Reid and shy!Reid. You see that a lot with other "awkward" characters (I've personally seen it in fics with Greg from CSI, Hiro from Heroes, and Dan from Gossip Girl).

I agree with the first post, saying he's somewhere in between. Slightly shy, but still pretty grown-up. He's just still kinda awkward. That, and MGG has said before he's bad at talking to women; I'm sure he lets that rub off in his character.