How old Xion is in Kingdom Hearts 3 is uncertain. Her age is an odd topic, to begin with, in 358/2 Days, where she is perhaps 14 or 15 years old to match that of Sora’s memories of Kairi. However, in Kingdom Hearts 3, when she returns, there are two ages she could be. 15 to match her original age since she was recreated here, or around 16 or 17 to match Sora’s age.