Nobody dies of "old age". As you become older, it is becomes harder to survive various diseases or afflictions. But where do you draw the line? If someone was to weak and fragile to leave their bed, and died due to no longer getting any energie from food, is that dying of old age? And what if they are to fragile to leave their cage?

If one is allowed to set timespan for "execution" to "however long it takes me to die of old age", then I argue it is also perfectly fine to take some liberty with the definition of "die of old age".