The extensions on the files (.gpi, .gbo, .gtx, .bot, etc) don't actually indicate anything about the gerber version. Different PCB CAD programs generate gerber files with different extensions, but their only purpose is to give the user a clue as to which layer they represent. So any of them should be usable, so long as you correctly keep track of the layers.
But I don't know if Eagle is capable of exporting to gerber X2. I'm sure ADS will be able to work with 274x, which is still the industry standard.