Minor signed in power of attorney. whether its valid r not?

My father, me and other paternal uncle and his two son given a  power of attorney on 2000 to my father's elder brother. I am only 16 years when i signed the power of attorney. Five members signed in  power of attorney document including me. Whether it is valid document on the whole since a minor signed in it? If its not valid . I like to know the way to inform it to sub register regarding this issue .