You are by all means no where near having the artistic skill level required to become professional concept artist.
Your work is still very elementary and lacks basic proportions.
I suggest you start drawing much much more. Do studies of what you want to draw from a professionally modeled or drawn pictures off the internet and I also strongly recommend that you try studying human anatomy above all if character concepts are what you are into.
This site has tons of reference material for artists, check out the Andrew Loomis Anatomy books they really do help alot.
http://www.fineart.sk/
And finally I'm going to give you a little motivation to get started drawing as soon as possible. This kid was 15 years old when he made these Halo ship concepts for a mod, he should be the user called 'Ring Leader', his real name is Ethan Nino,:
http://www.halowars.com/forums/4/114710/ShowThread.aspx
[Edited on 02.06.2011 10:54 PM PST]