  We construct average spectra of host galaxies of slower, faster, bluer, and
redder Type Ia Supernovae (SNe Ia) from the SDSS-II supernova survey. The
average spectrum of slower declining (broader light-curve width or higher
stretch) SN Ia hosts shows stronger emission lines compared to the average
spectrum of faster declining (narrower light-curve width or lower stretch) SN
Ia hosts. Using pPXF, we find that hosts of slower declining SNe Ia have
metallicities that are, on average, 0.24 dex lower than average metallicities
of faster declining SN Ia hosts. Similarly, redder SN Ia hosts have slightly
higher metallicities than bluer SN Ia hosts. Lick index analysis of metallic
lines and Balmer lines show that faster declining SN Ia hosts have relatively
higher metal content and have relatively older stellar populations compared
with slower declining SN Ia hosts. We calculate average $\rm H_{\alpha}$ Star
Formation Rate (SFR), stellar mass, and the specific-SFR (sSFR) of host
galaxies in these subgroups of SNe Ia. We find that slower declining SN Ia
hosts have significantly higher ($>5\sigma$) sSFR than faster declining SN Ia
hosts. A Kolmogorov-Smirnov test shows that these two types of hosts originate
from different parent distributions. Our results, when compared with the models
of \cite{childress14}, indicate that slower declining SNe Ia, being hosted in
actively star-forming galaxies, are young (prompt) SNe Ia, originating from
similar progenitor age groups.
