I don't see anything wrong with their relationship. No need to apply human standards and modern day humans standards to boot to alien cultures. I assume if your in Starfleet you see all sorts of things that go against human norms. One of the points of Starfeet is to learn and even come to accept these differences. Kes might be 2 by human standards but the Ocampa clearly have a whole different view on age which is to be expected when i you are lucky you might live to be 12 years.