Traditional Thai gesture.
There are many opinions and views on how and whom should you make wai. In fact everything is much easier if you are foreigner.
When doing wai to Royals or monks – put up your palms to the head, pressing your thumbs to the forehead and bow your head.
As everyday greeting wai is quite simple – index fingers barely touch the chin. Actually position of your index fingers at face level will show how much respect you pay to another person. As higher you put them up, then more you respect other person.
In Thai culture elderly people deserve more respect than others.