The article attempts to define the relationship between cognitive competences and identity styles in different periods of life: adolescence, early, middle and late adulthood. It also examines whether there are differences between the age groups in the dominant style of identity and in cognitive competences (formal and post-formal thinking). The 495 participants: 192 adolescents, 131 young adults, 91 adults and 81 seniors were tested in a baseline study using the Test of Formal Thinking (Horneman, Longeot) and the Identity Styles Questionnaire: ISI-3 (Berzonsky). In an additional pilot study, 281 participants: 166 adolescents, 87 young adults and 28 seniors were tested by means of the "Everyday problems" method (Sebby, Papini). The results show that early and middle adults in comparison with adolescents revealed a higher level of formal reasoning. In all age groups, the Informational Style of identity prevailed, followed by the Normative and Diffused styles, but with age the level of Commitment and the intensity of the Informational and Normative Style of identity changed. Among adolescents, there was a negative correlation between TOF scores and Commitment and Normative Style, while a positive but low correlation was found between the level of formal thinking and the level of Commitment in the senior group. The analysis of the results of the additional study in which the links between the identity styles and the level of post-formal reasoning were tested indicates that there is a stronger correlation compared to the measurement of the relationship between the identity styles and the level of formal thinking in each age group.