如果是培养你的恩师,不管现在如何,你依然尊敬和爱护他,这是下一代,受惠于前一代的起码的应有的品德.这是饮水思源,知恩图报,这才是孝的核心. If he is not a good father, or not a good teacher, not a good present, no '恩' for you. Do you still respect him when he is old? if you still do it, you are very traditional guy. I think less and less people will do that.
尊敬 everybody including older people should be the best rule.... You respect him, not because he is older, he is weak, he has more knowledge.
To bad my English ...
Happy holidays