Cold joints are stiff joints
A tortoise is an ectotherm, so his muscles and joints literally run at the temperature of his surroundings, and an elderly tortoise who is too cool will barely move at all. Before assuming the worst, check the basics with fresh eyes: is the basking spot holding its usual temperature, has the background heat slipped as the house cooled, and can he still reach the warm end easily? A longer warm-up under the lamp, and an enclosure arranged so the warm zone is close to where he sleeps, often returns a surprising amount of movement on its own.
Flatten his world
Rework the enclosure so nothing requires climbing: remove ramps, raised slate and steep-edged hides, or bury them so the step up disappears. Set the water dish at floor level with a shallow, grippy rim he can walk into rather than haul himself over, and choose a substrate he can grip — packed soil rather than smooth tile — because slipping saps confidence as much as stiffness does. Then arrange his day in a small circuit: shelter, basking spot, water and feeding area all within a few unhurried metres of each other.
Bring the food to him
A stiff tortoise who cannot patrol for food should find it where he already rests. Serve his weeds and greens on a flat slate at ground level, chopped or grated into pieces he can tear without bracing and pulling, and vary the pile — dandelion, plantain, clover, edible flowers — to keep appetite interested. If he eats slowly, leave the slate down for an hour or two rather than removing it on a young tortoise's schedule. Dust the food with his calcium supplement as usual and check his ultraviolet lighting is in date, because an old tortoise still needs to make vitamin D to use that calcium, and a faded bulb quietly undermines both bone and appetite.
Soaks and gentle exercise
A shallow, lukewarm soak two or three times a week does several jobs at once: it hydrates him, encourages him to pass waste, and the warmth loosens stiff legs enough for a short wander afterwards. Let him choose his pace on a safe lawn on warm days, following food trails of scattered leaves rather than being carried anywhere, and stop when he stops. Movement little and often keeps joints working; one long forced march does the opposite.
When stiffness is a vet matter
Age explains a lot, but not everything: book a reptile vet if one leg is clearly worse than the others, a joint looks swollen, the shell feels soft, he stops eating for more than a few days in warm weather, or he drags rather than lifts a limb. Joint wear, old injuries and bone problems can all sit behind stiffness, and several respond to treatment — but leave it to the vet to say which. Bring your notes: a KinsLe Pet Passport holding his weight trend, appetite record, mobility changes and past vet history turns that appointment from guesswork into a proper review of how he is ageing.