Actually, one might not be older than the other, in the case of the Corsair memory modules. Revision numbers have nothing to do with the age of the modules (in fact, version 1.1 could have been manufactured on the very same day as version 9.9 of that same model number, depending on the subcontracted assembly plant used); the only way to determine the age is the multi-digit lot number.
The revision numbers of those modules merely determine which actual parts are used in the RAM. The number to the left of the decimal point indicates the IC chips used on the modules - while the number to the right of the decimal point refers to the PCB (Printed Circuit Board) used in their manufacture. And there is some chance that the two different version numbers might not work well or at all when mixed together in the same system.