For the sake of argument, the year difference between Touko and Chie was actually greater than the year difference with Kiriyan and Masaki. But given that Masaki has a youthful charm to her, I think I see what you're saying? (At the same time, they did play off each other well in Osaka Samurai and Me and My Girl *shrug*)

The star system is a little weird right now in that older ones like Kiriyan and Yuuhi are finally getting their due, while at the same time, the up-and-coming ones are somewhat younger than usual. (I dunno, personally I'm of the belief that there always are a few up-and-coming upstarts and that it's not anything radically new)