What you need is a technique called wear leveling. It doesn't write your data every time at the same location in the EEPROM, but uses some algorithm to use different locations. I've read about complex wear leveling algorithms, but I wouldn't know why the following simple method wouldn't work.
Add to your data a 24-bit counter, so that your data block is for instance 8 bytes long. Pages on a 24AA64 are 32 bytes long, so a 64kb EEPROM holds 256 pages. From the datasheet:
"When doing a write of less than 32 bytes the data in the rest of the page is refreshed along with the data bytes being written. This will force the entire page to endure a write cycle, for this reason endurance is specified per page."
so it doesn't make sense to use data blocks smaller than a 32 bytes page.
Look at the counter of the first page. If it's zero you used the maximum number of write cycles for that page, so you move on to the next page and check that counter. Repeat until you find a counter > zero. That's the page you're currently using. Microchip's EEPROMs have a 1 million cycles endurance, which you can increase to 256 million with the given example of maximum 32 bytes per block in a 64kb EEPROM. That should be enough to outlast your product: 40 years if you write once every 5 seconds(!).
You'll want to initialize your EEPROM on first use. How do you know when that is. Use the last page to write a unique signature upon initialization. Check at each power-up if the signature is there. If it isn't the device has to be initialized. You can preset the counter in each page with 0xF4240 (for 1 million) or clear everything to 0xFF and write the 0xF4240 when you first use the page.
Initializing an EEPROM is needed because sometimes a certain pattern is written to it in the production process.
further reading
datasheet 24AA64
EEPROM Endurance Tutorial