The Brownlees grew up with the current system - they aren't that old you know
I do recall running a half marathon in around 1988 organised by Bacup Irish Club and they had age group races then on the main road from Bacup to Haslingden - I think Mark Aspinall, then of Rossy and now of Clayton won it. When you look at ladies races and that the 1500m was first run in the Olympics in 1972 then I would suggest that races tended to be shorter years ago.