  There is observational evidence of a dearth in core-collapse supernova (ccSN)
explosions from stars with zero age main sequence (ZAMS) mass M_0~17-30 Msol,
referred to as the 'red supergiant problem'. However, simulations now predict
that above 20Msol we should indeed only expect stars within certain pockets of
M_0 to produce a visible SN explosion. Validating these predictions requires
large numbers of ccSNe of different types with measured M_0, which is
challenging. In this paper we explore the reliability of using host galaxy
emission lines and the Halpha equivalent width to constrain the age, and thus
the M_0 of ccSNe progenitors. We use Binary Population and Spectral Synthesis
models to infer a stellar population age from MUSE observations of the ionised
gas properties and Halpha EW at the location of eleven ccSNe with reliable M_0
measurements. Comparing our results to published M_0 values, we find that
models that do not consider binary systems yield stellar ages that are
systematically too young (thus M_0 too large), whereas accounting for binary
system interactions typically overpredict the stellar age (thus underpredict
M_0). Taking into account the effects of photon leakage bring our M_0 estimates
in much closer agreement with expectations. These results highlight the need
for careful modelling of diffuse environments, such as are present in the
vicinity of type II SNe, before ionised emission line spectra can be used as
reliable tracers of progenitor stellar age.
