Well X is the first Reploid(zero isnt one) because the reploids are based on X
The Reploids are called Reploids because their technology is made from an attempt to replicate X. Seeing as it's impossible for X to have been made as an attempt to replicate himself, he can't be a Reploid.
Commander Zero.. would you like to use me as a pillow?Nah, it's OK. But stop blocking my sun.