My first Dragon Con was back in back in 2006. That makes me, according to some, a veteran attendee, but I still think you may as well keep calling yourself a newbie until well past your 15th Dragon Con.
The reasoning for that is simple- A veteran in many other endeavors is sometimes defined as someone who has been there and back enough times to have done and seen it (almost) all. Given the size of the convention, as well as the growth rate of the convention over the last six years, it’s impossible to really come close to doing that in six, seven, or even ten Dragon Cons.