The issue of age, especially with regard to employment relationships, is related to the principle of equal treatment and non-discrimination that has been set forth in numerous acts of international law, conventions of the Council of Europe and the European Union law. In the Polish law, this principle is expressed in Articles 32 and 33 of the Constitution. However, both Community and national regulations provide for exceptions to this rule, related, for example, to the maximum age at which certain professions can be practised, sometimes below the commonly binding retirement age. These exceptions are permitted when physical and mental fitness is necessary to do a given job. The article presents permissible forms of different treatment of employees because of their age. The author focuses on an analysis of cases when age is, in accordance with the law, the basis to end an employment relationship and to lose a licence to practise a profession. The article also presents legal regulations that provide for age limits for practising certain professions, and indicates the reasons for such regulations.