Stephen,
In my mind, eight years old is a pretty young age for someone to make a commitment of belief and of a determination to be faithful to the end of their life, but yet when I was eight years old, I remember feeling that I was sincerely making that kind of commitment and covenant, and I didn’t think I was too young to do it. When my youngest daughter was baptized, it didn’t seem like she was too young to make that kind of a commitment, and so it has been with each of my children. Eight years old seems like a “right age” for someone to be making a knowing, believing, self-chosen decision to be baptized. The parents may urge the child to be baptized, but they shouldn’t force it on them and the bishop interviews the child to see whether they are making a knowing, informed and self-chosen decision to be baptized. It seems like a “right age” for this kind of decision, in my way of thinking and in my experience.