If he has been in out of the weather it may be that he has poor circulation due to age. As with humans, the farther from the heart the poorer the circulation . It shouldn't mean he is ready to pass on soon if this is his only symptom but he might benefit from massage of his legs and feet, it may help get the blood flowing better. If he isn't already, you might try adding supplements for joint health and arthritis, those things wouldn't cause cold feet directly but they may keep him from moving as freely as he could and therefore limit circulation. I hope he is comfortable otherwise. Let us know.