  As a massive star evolves along the main sequence, its core contracts,
leaving behind a stable stratification in helium. We simulate 2D convection in
the core at three different stages of evolution of a $5M_{\odot}$ star, with
three different stratifications in helium atop the core. We study the
propagation of internal gravity waves in the stably-stratified envelope, along
with the overshooting length of convective plumes above the convective
boundary. We find that the stratification in helium in evolved stars hinders
radial motions and effectively shields the radiative envelope against plume
penetration. This prevents convective overshooting from being an efficient
mixing process in the radiative envelope. In addition, internal gravity waves
are less excited in evolved models compared to the zero-age-main-sequence
model, and are also more damped in the stratified region above the core. As a
result, the wave power is several orders of magnitude lower in mid- and
terminal-main-sequence models compared to zero-age-main-sequence stars.
