  We present extensive numerical investigations of the structural relaxation
dynamics of a realistic model of the amorphous high-temperature ceramic
a-Si$_3$B$_3$N$_7$, probing the mean square displacement (MSD) of the atoms,
the bond survival probability (BSP), the average energy, the specific heat, and
the two-point energy average. Combining the information from these different
sources, we identify a transition temperature $T_c \approx 2000$ K below which
the system is no longer ergodic and physical quantities observed over a time
$t_{obs}$ show a systematic parametric dependence on the waiting time $t_w$, or
age, elapsed after the quench. The aging dynamics 'stiffens' as the system
becomes older, which is similar to the behavior of highly idealized models such
as Ising spin-glasses and Lennard-Jones glasses.
