He was born in 1938. That makes him 75 now. On inauguration day he will be 78 and he'll be 82 at the end of his first term, if he lives that long. He doesn't look healthy right now.
Reagan was just short of 70 when first inaugurated.
Seriously, I agree with you that Panetta will not be running. There was a time that he was a thought a decent Democrat, but his ambition belied his “ aw’shucks “ mannerisms, as he sidled up to the Marxists.