When your cables were made, HDMI 2.0 wasn't finalized and thus they couldn't test/certify to that standard. Thus, the best they can do is claim 4K at 24Hz because that's was the only certification available at the time (based on the HDMI 1.4 standard).
The HDMI consortium has stated that all 1.4 cables should be compatible with 2.0 so you should be just fine. Unless you see degradation in quality your current cables are just fine.
It's like grabbing a DVD drive only to see it say "compatible with Windows XP". If you put the drive in Windows 7 it will work just fine. All that says is back when the drive was made, there wasn't a Windows 7 certification.