40 years before I was born is conservative.
I grew up reading watching Shining Time Station and reading The Railway Series. Oliver was one of my favorite characters (along with the stable of the MSR.) Finding out he was based on a real locomotive, easily modeled, was a revelation.
Honestly, the focus on 30's GWR is almost regrettable now, as I have always had a penchant for the odd, and ~1930 LMS is infinitely more appealing there. So, GWR in N and LMS in OO, where the oddities are often available.