The scope of article presented are refl exions on legal limitations concerning the age of natural persons undertaking actions within administrative procedure. There are four general, basic categories of such participants indicated in the article: party, party’s legal representative, witness and expert. The conclusion goes towards statement, that the criterion of the procedure’s participants’ age has different importance according to validity of their procedural activities. In the case of a party as well as party’s representative, their activities’ validity depend on the level of their ability to undertake legal activities which is connected to the age (age of 18 to obtain full ability to undertake legal activities and age of 13 for limited ability). The situation of witnesses and experts differs. In general their age does not influence the case. But it seems to be obvious that the young age implicates the way of perception and communication, as well as range of specifi c knowledge.