<h2>Dragons are mentally incapable of grasping how to read/write</h2>

The big turning point for mankind coming out of the stone age was literacy.  For over a  million years, man kind's ancestors survived by learning what they could from oral tradition alone. Without writing, it is just as easy to lose knowledge from one generation to the next as it is to gain knowledge.  So, you could be the greatest inventor in the world, but with no way to write it down, your inventions can never see wide-spread adoption, and most of them would be forgotten within a few generations.  

That said, the there is one way out of the stone age without writing which is apprenticeship.  Here, each dragon can pass on a specialized set of knowledge to the next generation.  Each generation will forget a bit and innovate a bit. Unlike a society that has a formal education system, apprenticeship will eventually find an equilibrium where new ideas become so complex that they can no longer be taught without a written record because they require the collection of too many unrelated concepts to orally aggregate in one place.  Chemistry for example is the culmination of the works of many great minds spanning several nations over several centuries to be able to come to the kind of system we have today.  In an oral society, those men would have never heard of each-other's work; so, instead of building up on previous discoveries, each person's work would be independently lost to the ages.

Without literacy, I doubt you could actually achieve Renaissance levels of technology, but you could probably get somewhere in the classical-to-medieval tech level just fine, and then stagnate... only it won't be true stagnation. Knowledge will just be in a constant state of ebb and flow.  Some centuries you might peak at Renaissance levels, then next century you regress to ancient level tech all because some master blacksmith had a heart attack and died before he could fully train the next generation.