Isn't he 17? He's 15 in KH1, 16 in KH2, and though the gap to KH3 is less than a year I sort of assumed Sora turned 16 and Riku turned 17. Assuming they follow a normal solar calendar (which is... certainly a concept), Sora's birthday is in March, Sora is 15 in KH2, and HPO are on summer vacation in Twilight Town in KH3... does that mean... shit, are HPO still on the same summer vacation as in KH2? time does not make sense in this series lol. Yea I guess in KH3 Sora is still 15 and Riku's probably still 16, though we don't know when Riku's birthday is.Riku is 16.
In either case, in present time (i.e., ReMind/Melody of Memory), a year has passed so everyone is a year older anyway
Also, never really considered Riku/Aqua, but I kinda love it tbh