Well....because when you sell a novel, you're really selling yourself. Your "brand". When I wrote my first book I was 17. At that time (2005) YA wasn't what it is now. I felt like it wasn't really respected (which was true, to an extent), and was always worried my work would be pigeonholed because of my age. Now, on the other side of it, I feel like I'm running out of time to sell myself as the "young author" who actually made it, ala Paolini, Atwater-Rhodes, etc, because I'm 25. Age shouldn't matter, but sadly sometimes it does.