User blog comment:Crimson Marauder/Origin of Vampires???/@comment-25942629-20151218150038/@comment-25942629-20151220024108

Only progenitors have permission to turn humans into vampires. I imagine this is in order to keep the vampire lineage strong. Therefore, a vampire turned by a progenitor can still be a noble. A vampire's strength is determined by two things: 1) his/her age, and 2) the power of the vampire who turned him/her.

Then, said vampire may become a progenitor based on his/her strength as a result of all of this,as I understand it. It is possible to be strong and not be a noble as well, such as with Lacus, Mika, and Rene.

We don't know a ton about the species of vampires, but the Guren's LN volume 6 reveals some after Mahiru becomes a vampire. Since Mika might be playing a larger role in the manga now, we may learn quite a bit more about vampires there. Mika's LN series should definitely enlighten us quite a lot as well.