The expected charge spectrum at the top of the atmosphere has been calculated for the charge interval between atomic numbers of 11 and 14. The calculations have been based on the assumption that cosmic-ray particles are selected by an ionization process from matter having 'normal' composition. The ratios Na/Mg, Al/Si and (Na + Al)/(Mg + Si) have been studied as a function of the amount of matter passed for different transport models and compared with experimental results. If the transport takes place at the constant energy of 800 MeV/n, the comparisons indicate a path length of about 4 g/sq cm for a slab model and a mean path length larger than or equal to 5 g/sq cm for an exponential model. The possibilities of using Al-26 to determine the age of cosmic rays have been discussed. The ratio Na/Al is found to be very advantageous for an age determination, but experimental data are not yet sufficiently accurate for this age estimate.