As One_Dead_Angel said "the way the 4 mainline techs work separately from the ages is brilliant and one of the most innovative things in RoN. It makes restricted and different age starts/end games much more balanced then if it didnt have this system."
I agree with that, and I actually checked default requirement of eah of the 4 mainline techs and I found out that the other three mainline techs: agriculture, food industry, carpentry... those economics upgrade actually don't require ages, only science level and previous upgrades of its own, BHG designed them to work that way.
But it's absolutely true the university upgrades' default requirement include the age, and it only applies in standard game setting.
It is annoying that if I want to design a scenario that prevents player to upgrade to higher univeristy techs, it's not possible unless I disable the tech, but the tech requirement actually says it requires that specific age but in the game it doesn't require.
If I add the age requirement of industrial age to food industry, it works when end age is classical, it will be not upgradable when end age is before industrial age.
But the age prerequisites for university upgrades are there but they don't work!!
so It's indeed a bug.