telynk, that seems reasonable--the bit about the contact between Atlantic and Mediterranean coastal peoples explaining the timing of the caravel's development. It suggests that if you want it earlier, either speed up Reconquista--or have a single Andalusian Muslim state stabilize earlier.
If contact between sailors who habitually sailed one sea or other were key though, what about Moroccan sailors? Some would have homes east of Gibraltar, others west of it--it raises the question why they didn't anticipate the caravel, any time between the first Muslim invasions of Iberia and the termination of the Reconquista.
Maybe what was needed was a fusion not just of any Atlantic type boats and Med type, but specifically boats from the northern Atlantic?
Even so, a stabilized Andalusia would probably do enough trade with lands to the north they'd get the merger of the types sooner or later--and sooner than OTL's Portuguese.
Now all this talk about a ship type obscures and distracts from the fact that there is more to seafaring than just the shape and structure of the boat, although that is clearly very important. But just as important is the development of the arts of navigation, and the development of means of storing food and water (or something drinkable) for long intervals out of contact with any land that could reliably supply these things. I've seen it suggested that the development of "hardtack" biscuit, which is really a sort of pasta, was a critically important step in enabling European long-range sea trade and eventual sea power. And of course the Portuguese age of discovery and construction of their trade and defensive networts was famously launched by Prince Henry the Navigator, who strove to systematically advance the scientific state of the art of all things related to seamanship. Did the caravel cause Portuguese to realize the importance of getting that science done, and support it in the person of a prince? Did the caravel in fact take its final design from the guidance of Prince Henry's studies? Did both efforts wait patiently until a means was known for storing food and drink more than a month or so, or was hardtack and suitable solutions for storing drink the outcome of a desperate search for storable provisions once there were ships that could outrun older forms of supply?
Even if we can identify which innovation is the root and which the branches, it should be clear that all of these things have to be possible in order to conduct the voyages the Iberians began to accomplish in the 15th century. This suggests to me that there would be a time and place for them, and we cannot freely imagine the package just happens to be stumbled upon any arbitrary century we like. Classic Dynasty Egyptians can't do it, Minoans can't do it; the Romans can't do it and apparently even the Carthagenians (who one gathers used to trade even as far as Cornwall) never came near doing it and I'd say surely could not. It is part of a package of developing technical capability that associates it with a certain level of development and a certain range of centuries in certain times and places.