What might the use of the discpline wand on the elderly suggest about the community and human nature?
I don't know if this is what you mean by human nature, but here goes:
I think that the use of wand means that it is human nature for older people to lose their inhibitions to some extent and become more like children. It is often the case that older people stop worrying as much about how they will be perceived and start acting more how they want to act.
What the use of the wand says about the community is that even the old are not allowed to be different. The members of the community must keep their inhibitions -- they must always act in the expected ways, no matter if they are young or old.
In the book "The Giver" as people age they are no longer really of value to the community. In order to keep them following the rules and doing what they are supposed to do the rods are used to control and discipline the elderly.
The community in the book has already left behind those things that make-up humanity. Everything in the community is the same, but children and the elderly have no rights. They are released to death without their desire. The adults are treated like they are worthless. There is no sense of them having any self-worth or value to those around them. They do not recognize that the use of the rod is unfair and bad just like they accept releasing someone to death is acceptable.