If they are trully juveniles, yes, they may take a long time to reach adulthood, which is the point where they go back to water. Mind you, some grow faster and reach adulthood within a year.
However, if you are buying from a pet-shop there´s a 99,9% possibility the animals are WC adults (unless he is breeding his own orientalis which is extremely unlikely for a pet-shop owner).
People have been reporting that C.orientalis are appearing in shops with small size and looking like juveniles, but as far as i´ve ben able to ascertain they are in fact young adults. People just don´t realize how small young adults can be.
Anyway, if they are young adults, they can be kept 100% aquatic.
I would like to recomend you not to acquire WC animals. Many are ill, some are down right, dying, and the rest are at the very least VERY stressed due to the whole process of the importation from China. In short, even the healthy looking ones may develop infections or refuse eating and starve.
In adition, buying from the WC market promotes the capture and imporation of more animals. The ones you buy will be subtituted by more poor WC animals...
Before you decide, since you have some time until you learn enough(ALWAYS learn as much as you can before you even think about buying an animal), you may want to se if someone in NZ is breeding these newts and can give you, or sell you, some nice, healthy, CB ones.