Space Age Compatibility?
Yes! Currently it is able to work out of the box for Space Age. The Fliers still follow the logic for the spitter spawner, so you will only see them on Nauvis for now (ooh, a hint at an update??)

What do you mean, "They don't fly over water normally and ERM changes it?"
Enemy Race Manager has proper AI for enemies that are considered "Flying" by the game and uses custom logic for the enemies in the mod.
The base game has this logic system too, but Wube never has an enemy that flies over terrain so there isn't anything regarding that situation. Due to this, the Fliers follow the basic rules for Biters/Spitters. They will form groups and make a path along the terrain to the target area and will follow it. However when aggro'd they don't follow the exact system and instead will just charge at their target. It's the reason why the Fliers will stick in a "group" with the grounded biters and spitters and wont try to path over lakes and rivers. You may occasionally see a Flier go over the water randomly, but this is due to them pathing from one nest to another, and it doesn't calculate a path because it doesn't get stuck on anything so it just beelines it to the other nest.

Does it work with....?
Rampant - Yes but there's bugs. They will spawn briefly before the vanilla spawners get replaced by the Rampant spawners, but they do not spawn on Rampant spawners.
Enemy Race Manager - Unknown. As ERM has not been updated yet to 2.0, and this mod uses ERM's old compatibility code if ERM makes changes to it's codebase this mod may or may not have issues.
Armoured Biters - Yes! They compliment well.
Big Monsters - Unknown. No Crashes though.