Considering the gender identity as a crucial aspect of the culture that shapes our daily life and recognising the research gap on this topic in the context of sustainable education, the paper describes the quantitative cross-sectional study on gender identity of students and teachers comparing the respondents by their age and sex. Three age groups (106 female and 62 male) participated in the study: 18-19-years-old pupils from comprehensive and vocational schools (n=59), 20-15-years-old university students (n=52) and 24-64-years-old teachers working at respective schools and universities (n=57). The original Bem Sex Role Inventory was administered to measure the individual gender identity types of masculinity, femininity, and androgyny. The majority of respondents from all age and sex groups described themselves as androgynous. Male and university students featured the scattering of scores more toward masculinity, while the scores of female, pupils, and teachers were more inclined toward femininity. No statistically significant differences were found among the three age groups, while sex appeared to be more influential factor causing significant differences between male and female in terms of gender identity with male's inclination toward masculinity and female's inclination toward femininity. Dominance of androgynous individuals challenges the current approaches to the gender education in the context of sustainable development.