One of my scratch drives in my NAS (which was the boot drive until I upgraded the PC) is at 39% wear which alarmed me, until I realised that's after 3.6 years. Which considering its a bargain basement Crucial P1 500GB, that's really not bad.
The P3 2TB which replaced it as the boot drive only 8 months ago is now at 2% which again can seem scary seeing a number go up, until you realise that's 33 years if accurate. I'm sure something else will fail on the drive before the NAND at that rate.