There are many factors that will determine how soon wear will show on the Tennifer finish of the Glock pistols. My primary is a G 23 with over 20k rounds through it. There is only minor wear on the barrel . The paint on the slide stop lever is worn, but other than that, the gun is in very good shape.
If you have specific questions, I'd recomment you contact Glock directly. I have a friend who noticed abnormal wear on the barrel of his G 17. He contacted Glock and was instructed to send the barrel and slide back to them for refinishing. When he got the barrel and slide back, they appeared to be "factory new" and they installed Glock night sights free of charge.
gf