PIs it permissible for a younger person to bow to an older person when greeting them?

Praise be to Allaah.

It is not permissible to bow when meeting
someone, whether he is a scholar or anyone else.

Shaykh al-Islam Ibn Taymiyah (may Allah have
mercy on him) said:

With regard to bowing when greeting someone, it
is forbidden as is narrated in at-Tirmidhi from the
Prophet (blessings and peace of Allah be upon
him); they asked him about a man who meets his
brother, can he bow to him? He said: “No.” And it
is not permissible to bow or prostrate to anyone
except Allah, may He be glorified and exalted, even
though that may have been a form of greeting in
other religions, as in the story of Yoosuf –“…and
they fell down before him prostrate. And he said:

‘O my father! This is the interpretation of my
dream aforetime!’” [Yoosuf 12:100]. But in our
religion it is not acceptable to bow or prostrate to
anyone except Allah; in fact it is also forbidden to
stand as the non-Arabs stand before one another,
so how about bowing and prostrating? Similarly, a
partial bow is also included in this prohibition.

End quote fromMajmoo‘ al-Fataawa, 1/377
And he said:

With regard to lowering the head when meeting
prominent figures such as shaykhs and so on, or
kissing the ground and so on, these are things
concerning which there is no difference of opinion
among the imams that they are forbidden. In fact
merely inclining the back to anyone other than
Allah, may He be glorified and exalted, is
forbidden. In al-Musnad and elsewhere it is
narrated that when Mu‘aadh ibn Jabal came back
from Syria, he prostrated to the Prophet (blessings
and peace of Allah be upon him), who said: “What
is this, O Mu‘aadh?” He said: O Messenger of
Allah, I saw them in Syria prostrating to their
bishops and patriarchs, and they narrated that from
their Prophets. He said: “They are lying, O
Mu‘aadh; if I were to instruct anyone to prostrate
to anyone else, I would have instructed a woman
to prostrate to her husband because of the
greatness of his rights over her. O Mu‘aadh, do
you think that if you were to pass my grave you
would prostrate?” He said: No. He said: “Do not do
that,” or words to that effect.

To sum up: standing, sitting, bowing and
prostrating are due only to the only One Who is
deserving of worship, the Creator of the heavens
and the earth; with regard to that which is due only
to Allah, no one should have any share in it; this
also applies to swearing by anything other than
Allah, may He be glorified and exalted.

End quote from Majmoo‘ al-Fataawa, 27/92, 93
The scholars of the Standing Committee said:
It is not permissible to bow when greeting or to
take off one’s shoes for him.

And they said:
It is not permissible to bow when greeting a
Muslim or a kaafir, whether with the upper part of
the body or the head, because bowing is a form of
worship, and worship can only be for Allah alone.

Shaykh ‘Abdul-‘Azeez ibn Baaz, Shaykh ‘Abdur-
Razzaaq ‘Afeefi, Shaykh ‘Abdullaah ibn Ghadyaan,
Shaykh ‘Abdullaah ibn Qa‘ood
Fataawa al-Lajnah ad-Daa’imah, 1/233, 234,Anas (May Allah be pleased with him) reported: A man asked: "O Messenger of Allah! When a man meets a brother or a friend, should he bow to him?'' He said, "No.'' The man asked whether he should embrace and kiss him? The Messenger of Allah (PBUH) replied, "No.'' He asked whether he should hold his hand and shake it? The Messenger of Allah (PBUH) replied, "Yes.''

[At-Tirmidhi]. , Surat Hajj Vs 18
22|18| See you not that to Allah prostrates whoever is in the heavens and whoever is on the earth, and the sun, and the moon, and the stars, and the mountains, and the trees, and Ad-Dawab (moving living creatures, beasts, etc.), and many of mankind? But there are many (men) on whom the punishment is justified. And whomsoever Allah disgraces, none can honour him. Verily! Allah does what He wills.

And Allah knows best.