I'm not sure you should change this. Artillery appears at level 13, supposedly in 1497. Of course, it looks late at first sight, as efficient cannons and bombards (meaning those which could be able to breach fort walls during sieges) were used in Europe starting from around 1415 / 1430. I would even say, if you consider Chinese history, artillery should be available from the beginning. Nevertheless, I think it's better to give an edge only to countries that deserve it, if you think that's not enough, rather than making it available earlier for everybody. As an example, if you put it earlier, I guess that some countries from exotic group, especially if human played, could get it around 17th century, which is not desirable. Of course, you do what you want, as you do it for yourself, and anyway you are much more skilled than I am. Just that I find it interesting to know what you think about that.