The SD Association says a typical card should last about 10 years with "normal usage," but (a) that's coming from the industry's website, and (b) they don't really say what "normal usage" is. Others have mentioned increased failure rates after about 5 years. On top of that, counterfeit and defective cards are relatively common these days.
And you're using a Samsung Note 3--from my experience on these forums for the past 2 years, I've seen a loooooooot of posts about SD cards that were messed up by Samsung devices, so it's possible it was an issue with the device rather than the card.