To honour an old man is incumbent. What if the old man shaves his beard, dyes his hair black and pretends to be young?

Answer

The order for honouring applies to a pious human being, not to a shaitaan. The old man you have described is a shaitaan. He may not be honoured. Honouring a faasiq causes the Arsh of Allah Ta'ala to shudder with disgust. Rasulullah (sallallahu alayhi wasallam) said: "The noblest of your youth are those who emulate old men, and the vilest of your old men are those who emulate young men." It is not permissible to honour a faasiq even if he is an old man.