Well just because the voice actress is 34 years old, doesn't necessarily mean that the character will be the same age as the voice actor. Lots of women have voice acted for characters who were very young, sometimes even voice act for boy characters.
I do hope Kiara in The Lion Guard will be an adolescent or adult in the show, otherwise I would think that is kind of weird that Kion was supposed to already be born during the events of Simba's Pride.