The term 'KIND OF AGE' can be solved by the crossword solutions of MENTAL (6 letters) and TEEN (4 letters). MENTAL age is a concept used to measure a person's cognitive development in comparison to the average development of their chronological age. It is often used to assess the intellectual development of children, and is calculated by comparing the individual's performance on tests to the average performance of others of the same age. Teenage years are the period of life between childhood and adulthood, usually considered to be between the ages of 13 and 19.