Hibernating naturally hibernating tortoises is something of a contentious issue among tortoise keepers, with many a varying opinion on the subject. Some believe that tortoises that hibernate naturally should always hibernate, while others argue that it is only necessary for breeding adults. Though it is true that these torts will only breed when hibernated and given an impression of seasonal changes, it has been sufficiently demonstrated that animals that don't hibernate suffer long term health problems in the form of liver and kidney malfunction. Also, animals that don't hibernate will often suffer the seasonal ups and downs regardless, as it is difficult to shield them entirely from changes in the seasons. They will recognize the shortening of the days through windows, for instance, and their demeanor will generally be more subdued indoors than out (presuming you keep them outdoors during the summer, which is often best, I find, though this depends upon one's locality). The thing is that if you are to hibernate an animal as young as yours, you must ensure that you have a refrigerator fitted for the job.
To successfully hibernate a tortoise, one needs these things: a refrigerator placed in a room with a relatively constant temperature, one that doesn't vary more than twenty degrees; a dual temperature digital thermometer with a working probe and a HI/LO memory function so one may map temperature fluctuations; a plastic box with holes drilled in the lid, large enough to comfortably fit the tortoise (if the tortoise can turn around in the container and be completely covered by the substrate, it is large enough); a substrate material such as peat moss and sphagnum moss in combination, deep enough to allow the tortoise to thermoregulate by burrowing; a scale and container to be used as a water tray should such be necessary.
If you have a reliable book on the subject, or if you have researched articles on the subject, I'm sure you can take it from here. If not, do post further inquiries. Putting the animals into hibernation and pulling them from it is always a maddeningly tense affair when you first do it, and there are always surprises waiting when it comes to tortoise keeping, but it eventually becomes standard practice once your tortoise cycles into the refrigerator routine.
T.G.