ECC the max coin age for PoS is 84 days (minimum being 42 days)
So, if you don't open the wallet for say, 100 days, only the 84 days age will be counted for your % stake . It is therefore desirable (but not essential) to open the wallet at least once in 84 days.'
@HOSTMASTER: That's bad advice, right? If someone opens the wallet and they had coins that were 40 days old, those coins will remain 40 days old. If they open the wallet again 84 days later, those coins would then be 124 days old, but they would only get interest for 84 days. So "...at least once in 84 days" is bad advice, I think.
Really you should open the wallet every 42 days, because the window where you can collect interest is 42 days long, not 84 days long. I've been saying "one month" because it's easier to remember and mark on your calendar.