Answer
Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- There is nothing wrong with kissing the hands of righteous people.
2- As for bowing down to greet people, it is prohibited. But if the bowing is not an act of veneration, rather one bows because he is short or paralyzed and the one who is greeting him is tall, so he leans forward to shake hands with him, then there is nothing wrong with that.
Answering your question, the late Saudi scholar, Sheikh Ibn Baz (may Allah have mercy on him) stated:
With regard to kissing the hand, the majority of scholars are of the view that it is makruh (disliked), especially if it is a habit. But if it is done sometimes on some occasions, there is nothing wrong with that in the case of a righteous man, a righteous ruler, a father and the like.
Some of the scholars regarded that as haram (prohibited) if it is customarily done at every meeting. But if it is done occasionally then there is nothing wrong with it.
As for putting the forehead to the hand as a kind of prostration on the hand, this is a prohibited kind of prostration and the scholars call it the lesser prostration.
But kissing it with the mouth, if that is not done as a habit, but rather rarely or occasionally, there is nothing wrong with it.
It is narrated from the Prophet (peace be upon him) that some of the Companions kissed his hands and feet. The matter is not serious if it is done rarely, but if it becomes habitual and is always done then it is makruh or haram.
As for bowing, that is not permissible. If it is like ruku` (bowing in prayer), it is not permissible, because bowing is an act of worship.
But if the bowing is not an act of veneration, rather he bowed because he is short or paralyzed and the one who is greeting him is tall, so he leans forward to shake hands with him, then there is nothing wrong with that.
But if he bows or leans forward out of respect for him, that is not permissible, and there is the fear that it may be shirk (disbelief) if the intention is to show respect and honor thereby.
To sum up, it is not permissible at all to bow to any person, kings or otherwise, but if it is not done as a sign of veneration, rather a person leans forward to greet another if he is short or paralyzed or is sitting down, so he leans forward to greet him, there is nothing wrong with that.
Almighty Allah knows best.
Source: www.islamqa.info