Piaget, the learning cycle

Today a link about Piaget and his theory about concepts.
http://scied.gsu.edu/Hassard/mos/2.8.html
In the stages schema that the author provides notice the mentionning of theoretical thinking and the absence of the word concept. Does conceptual thinking develop from beginning to after childhood?
note to myself: the ages that are listed I consider indicative and the remarks on the developmental order how the development occurs is not always as described. Why? Does this difference in order reflect the opposition sequential / associative thinking style? which is a relative opposition.