First, the decision itself belongs with your vet
Many elderly tortoises hibernated safely for decades, but age, old injuries and a declining condition can tip the balance. Have your exotics vet weigh in before winter on whether this tortoise should hibernate at all, and if the answer is to keep it awake, commit to that fully — a tortoise kept in a half-way state, too cool to eat but never properly asleep, fares worst of all. An overwintered tortoise needs the keeper to supply the warmth, light and routine that hibernation would have suspended, every day until spring.
Light and warmth that imitate a kind season
Set a basking lamp over one end of a roomy indoor pen, giving a genuinely warm spot to bask in with a gradient down to a cool retreat, and pair it with a proper ultraviolet tube or lamp positioned and replaced as its maker directs — winter health is built on that light, governing appetite, activity and calcium use. Run lights on a timer for a consistent day length so the tortoise's rhythm settles. Guard against the room's own cold: floors chill from beneath, so raise the pen or insulate under it, and check temperatures at tortoise height on the coldest evenings, not just mild afternoons.
Arrange the pen for an old body
Elderly tortoises stiffen, weaken at the legs and tire quickly. Lower every barrier: a water dish with a shallow, easy lip it can step into without climbing, food served on a flat slate at ground level rather than in a bowl, hides it can walk into rather than squeeze under. Keep substrate deep enough to dig and cushion joints, slightly moist in depth, and remove ramps or steep edges that a young tortoise would shrug off. Place food, water and the basking spot within a short, easy circuit — an old tortoise that must trek the length of a pen for each need will quietly start skipping some of them.
Feeding, soaking and the slower rhythm
Offer the normal leafy, fibrous diet daily but expect a reduced, fluctuating appetite in midwinter even with good light, and judge intake over a week rather than a day. Lukewarm shallow soaks two or three times a week encourage drinking and passing waste when the tortoise is moving less, and give you a regular close look at eyes, nose and skin. Handle gently and briefly, supporting the whole shell, and let rest be the default — winter indoors for an old tortoise should feel unhurried, with your role mostly quiet provision and observation.
Watching for the changes that matter
The risks of an indoor winter are quiet ones: steady weight loss hidden under a routine that looks unchanged, dry or closed eyes in heated indoor air, a runny nose, or joints so stiff the tortoise stops coming out to bask. Weigh monthly on the same scales and write it down with a line about appetite and activity, alongside the vet's overwintering advice. Call the vet if eating stops for more than a few warm, well-lit days, breathing sounds wet or effortful, or weight slides month after month — caught early, most winter problems in an elderly tortoise are adjustments, not emergencies. Kept through the winter in the Pet Passport on KinsLe, those monthly weights and notes turn spring's first check into a review of evidence rather than a guess.