Theoretical particle deposition studies for children and youths in practical health physics or medical aerosol therapy require detailed information on alterations of anatomical as well as physiological parameters during postnatal growth. Based on the commonly used anatomical model A of Weibel, assuming regular dichotomy, for an adult human lung, a mathematical model was developed for the calculation of airway parameters, such as geometrical dimensions and number of airways as functions of age. Sometimes widely scattered experimental data obtained by different authors were fitted to analytical functions by a multiregressional procedure. Due to the lack of these data for most of the generations of the anatomical model, theoretical considerations had to be applied. For changes of respiration parameters with progressing age, e.g., tidal volume or respiratory frequency, also experimental data were used. The results of these calculations can then serve as a base for the determination of deposition probabilities in different regions of the human respiratory tract.