  In this paper, we analyze the spectral energy distributions (SEDs) of 17
powerful (with a spin-down luminosity greater than $10^{35}$ erg s$^{-1}$)
young (with an age less than 15000 yrs) pulsar wind nebulae (PWNe) using a
simple time-independent one-zone emission model. Our aim is to investigate
correlations between model parameters and the ages of the corresponding PWNe,
thereby revealing the evolution of high-energy electron distributions within
PWNe. Our findings are as follows: (1) The electron distributions in PWNe can
be characterized by a double power-law with a superexponential cutoff; (2) As
PWNe evolve, the high-energy end of the electron distribution spectrum becomes
harder with the index decreasing from approximately 3.5 to 2.5, while the
low-energy end spectrum index remains constant near 1.5; (3) There is no
apparent correlation between the break energy or cutoff energy and the age of
PWNe. (4) The average magnetic field within PWNe decreases with age, leading to
a positive correlation between the energy loss timescale of electrons at the
break energy or the high-energy cutoff, and the age of the PWN. (5) The total
electron energy within PWNe remains constant near $2 \times 10^{48}$ erg, while
the total magnetic energy decreases with age.
