Are you 100% positive of this? Not trying to be rude, this just seems a little too good to be true. Kudos to glock if so, but I've never heard of anyone giving a lifetime warranty on something such as night sights that clearly will not last a lifetime.
Did you actually do this or were with someone when this happened?
I had new nite sites installed on three Glocks at the same time. I asked the armorer how long the warranty was and he said,"if they go bad we will replace them for free since we don't keep a record of when you bought them". The warranty that is stated is 15 years, but if they have no record I would bet he told me the truth. The age of the gun has no bearing since you can take an older gun in and have the sites installed. How are they going to know if you had them installed when the gun was new or when it was ten or more years old? The confusion comes from people that take a gun in with non Glock sites to have them replaced, they don't replace other brands for free.