The problem of the dependence of the didactic complexity of the studied concepts and theoretical models on the age of the student (schoolchild, student) is analysed. The complexity of a concept (term) can be characterized by the number of words from a fifth-grader’s thesaurus needed to explain its meaning. To find the complexity of a theoretical model of an object (for example, an atom), it is necessary to sum up the complexities of all the words that make up the description of the model and take into account the indicator of the variety of terms. Dependency graphs were built: 1) the complexity of the most difficult terms for understanding from the year of study; 2) the complexity of various theoretical models of the atom from the year of study at school and university. In both cases, the resulting curves are ascending, like a parabola, corresponding to an increase in complexity by almost a hundred times.