  In this Letter, using classified 197 supernovae (SNe) Ia, we perform an
analyses of their height distributions from the disc in edge-on spirals and
investigate their light-curve (LC) decline rates $(\Delta m_{15})$. We
demonstrate, for the first time, that 91T- and 91bg-like subclasses of SNe Ia
are distributed differently toward the plane of their host disc. The average
height from the disc and its comparison with scales of thin/thick disc
components gives a possibility to roughly estimate the SNe Ia progenitor ages:
91T-like events, being at the smallest heights, originate from relatively
younger progenitors with ages of about several 100 Myr, 91bg-like SNe, having
the highest distribution, arise from progenitors with significantly older ages
$\sim 10$ Gyr, and normal SNe Ia, which distributed between those of the two
others, are from progenitors of about one up to $\sim 10$ Gyr. We find a
correlation between LC decline rates and SN Ia heights, which is explained by
the vertical age gradient of stellar population in discs and a
sub-Chandrasekhar mass white dwarf explosion models, where the $\Delta m_{15}$
parameter is a progenitor age indicator.
