AIX since 1986
Well. I doubt very strongly that there are any 6150/1 systems running in anger any more, or any PS/2's running AIX PS/2 or mainframes running AIX/ESA, so they really only need to worry about POWER boxes, and they started in 1990. That takes out anything before AIX 3.1.
And since then, the Microchannel architecture AIX boxes can't run a supported version of AIX, nor can any 32 bit POWER systems or any with RS64 processors, so they really only have to worry about 64 bit CHRP systems that run AIX6.1 and later. That means that they only have to worry about systems built since about 2000! And as the basic OS running under 6.1 and 7.1 is not really different under the covers, and basically is compile once/run anywhere, it's a much smaller target than Solaris or HP/UX.
So a bit of diversion going on here to detract from the fact that they really must be a bit thick!