Bowing to anyone other than Allaah is haraam
Question

                Is it permisible to bow while greeting a respectable/elder person/parent Other than saying "As-salam Alaykum Wa-rahmatullahi Wa-barakatuh".
Praise be to Allah.The usual greeting is “Assalaamu 
          ‘alaykum wa rahmat-Allaahi wa barakaatuhu (Peace be upon 
          you, and the Mercy of Allaah and His Blessings), because Allaah says 
          (interpretation of the meaning): 
“greet 
          one another with a greeting from Allaah (i.e. say: As-Salaamu 
          ‘Alaykum — peace be on you), blessed and good”
[al-Noor 24:61] 
          
The ahaadeeth explain this greeting 
          clearly. 
 But bowing is not permitted, unless 
          the person being greeted is old and is unable to stand up, or is one 
          of your parents and you do not want to make him or her stand up to shake 
          your hand or embrace you. So if you bow and kiss his head or forehead 
          out of respect for the rights that he has over you, then this is not 
          the kind of bowing that constitutes an act of worship. Undoubtedly bowing 
          is an act of worship towards Allaah, as in rukoo’ (the bowing in prayer), 
          so if that is done without shaking hands or kissing, it is an act of 
          veneration towards that person and is therefore shirk.