In this Letter, using classified 197 supernovae (SNe) Ia, we perform an analysis 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 ~10 Gyr, and normal SNe Ia, which distributed between those of the two others, are from progenitors of about one up to ~10 Gyr. We find a correlation between LC decline rates and SN Ia heights, which is explained by the vertical age gradient of the stellar population in discs and a sub-Chandrasekhar mass white dwarf explosion models, where the {Delta}m_15_ parameter is a progenitor age indicator.

Cone search capability for table J/MNRAS/520/L21/tablea5 (Data on 197 SNe Ia and their 196 hosts)