How old should the people involved in this project be?

I would recommend that participants be no younger than 8 years old. One of the things to consider when deciding who should participate in the project is the age of the participants. I have found that most kids, even very young kids can learn to play the flute. But young children have a short attention span and don’t do as well with flute making. They require too much assistance which can be hard on the supervisors. I once taught a group where some of the participants were as young as 6! It can be done, but it is not easy!
We have found that 8 year olds usually have the attention span necessary to be successful in these projects. There is no upper age limit. We have done a number of projects where senior citizen carving groups have made flutes. When you have a group with participants of varying ages the older people can help the younger people. It is always helpful to have a few adults available to supervise and help if necessary.