  The concept of "age" as a parameter for the description of the state of
development of high energy showers in the atmosphere has been in use in cosmic
ray studies for several decades. In this work we briefly discuss how this
concept, originally introduced to describe the average behavior of
electromagnetic cascades, can be fruitfully applied to describe individual
showers generated by primary particles of different nature, including protons,
nuclei and neutrinos. Showers with the same age share three different important
properties: (i) their electron size has the same fractional rate of change with
increasing depth, (ii) the bulk of the electrons and photons in the shower
(excluding high energy particles) have energy spectra with shapes and relative
normalization uniquely determined by the age parameter, (iii) the electrons and
photons in the shower have also the same angular and lateral distributions
sufficiently far from the shower axis. In this work we discuss how the
properties associated with the shower age can be understood with simple
arguments, and how the shapes of the electron and photon spectra and the
relative normalization that correspond to a certain age can be calculated
analytically.
