USB drive has expected lifespan of 10 years which I do not think it is bad at all.
What makes the lifespan of USD drive, CD, DVD, SSD or HDD shorter or longer depends on how often you are using it to transfer files, and also maintenance. If he is using the USB drive for just file backup and nothing more, I am expecting the USB flash drive to have a long lifespan if he protects it.
10yrs is just the expected lifespan but in my experience, it doesn't most of my USB Drives no longer work after a year or two some of them work but files become corrupted even though I take care of them very well.
Only 2 of my 8 USB drives with two different brands still survive after 4 years(transcends 16GB and Sandisk 32 GB).
Having multiple backups is also fine but for long-term DVDs is way better to handle files for more than 10 years because I have a DVD that still survives after 10 years it still works.