Indeed, I can't get my head around that sort of thing at all. 1980 still seems "modern" (ish) to me, 1940 seems like the deep, deep past (perhaps just as well given what was going on then).
In a similar way it's hard to get my head round the fact that many of the 4SUBs, in their final months of service when I first started using the railways regularly (I think I saw one in service from a distance, and more going ECS to possibly Eastleigh on withdrawal) were less old then than the 455s or 150s are now!
If we move on another 10 years to 1990 (which really does seem modern - hey, the ECML was electrified!) it's equally strange to think that going back the same number of years gets us to 1958.
And of course, talking this way in itself is another sure sign of getting old.
I don't think I'd go as far as saying 'the deep, deep past' -- my parents were around in 1940, and old enough to remember it, and are still around now -- but 1940 certainly seems like another era from the one that contains both 1980 and now. And (apart from ECML electrification not being completed to Edinburgh until 1991) I agree with the rest of what you say.
To be fair, on the railways at least I think there probably genuinely was more change in the 10 or 20 years before you and I were born than in any comparable persiod, earlier or later, since about 1850. And some argue that many Southern slam-door units were already old-fashioned when built, and so would feel old -- certainly a 4-SUB seems much less modern than 1938 tube stock.
In 2015, when it was the centenary of whatever happened in WWI in 1915 (Gallipoli, I think) and the bicentenary of the battle of Waterloo, I remember finding it strange that 1915 (practically Victorian) was only twice as far away as 1965 (only a few years before I was born and therefore quite recent); but 'zooming out', I also found it strange that 1815 was only twice as far away as 1915. It doesn't seem that long since I remember talking to people who were of an age to remember 1915, and although some things that we take for granted had not yet been invented/discovered then (e.g. computers or antibiotics), much modern technology in transport, communications, medicine, etc. already existed (albeit in some cases, like aeroplanes, only in primitive form); whereas in 1815 although stationary steam engines were fairly well established, powered transport was in its infancy, telecommunications were limited to a few optical telegraph routes, and anaesthetics and germ theory were still in the future.
