I doubt Aono's older than Matsuri given the fact that Matsuri revived Aono. But, in terms of power, that's debatable. On one hand, Matsuri can revive life and decay/deteriorate objects. On the other, we see Aono having the ability to give life to inanimate objects (such as the origami frog) and possibly reviving or recreating Yorito. I have yet to see Aono do anything along the lines of deteriorating objects or biological matter.
So, who's more powerful? If going by the saying, "The older you are, the wiser you get," then I'd say Matsuri is the wiser and more powerful of the two. However, she seems just too kind and gentle to harm anyone. She doesn't want to hurt anyone, especially Yorito. Aono, however, could be the more powerful
seeing that she used her powers to possibly the full potential of a Yaka-- much more than Matsuri. Again, this is basing it on watching Ep.6 and 7 now.