For an agressive civ, it could be fun to access one age earlier building who cost only wood.
Unit and tech aren’t available before the standard age tree.
For example during you feodal age research, you can build blaksmith and archery range.
Imo this is only relevant for stables and monasteries as for the other buildings you usually don’t get a benefit from having them earlier, only if your macro was bad and you have too much ressources to spend.
But then your timings are bad already so you don’t really win something, just lose less.
(1 range archers could be beneffitet a bit also, but it’s marginal)
But I would like to see this for stables. It’s even potentially a tweak to the core game that you can place the stables earlier for a better timing on your scout rush.
I got Khmer vibes. If you doing a FC build order, then you can add some extra vills in dark age. Add feudal building during researching feudal age and you can instantly go to the castle age without adding any vills in feudal age. So your basic 25+2 FC build, will become a 27+0 FC build. Or maybe you can even get away with a 26+0 FC build.
Novel idea, but too weak to be very interesting. Basically a high early investment with only a slight timing payoff once you reach the next age and get to use the buildings
The idea is good. It would indeed be way too OP on stone costing buildings. But without it, it feels a little bit underwhleming.
Two suggestion to spice it up more:
the same civ could also have one of these two other bonuses:
All techs are available one age earlier, however the effect does not apply before the proper age is reached.
Stone costing building can be built up to 99% one age earlier (except walls).
For the latter one, it allows you to be more unpredictable with your tower/castle drops. Though you need a good timing otherwise your villager will stop working at 99%.
Though for all this, there would be a big implementation challenge for the devs…