There's a source claiming 10 years as an upper limit. I've seen 8 year old neons that were still happy and lively. I suspect that most have very short lives in captivity due to the fact that most are kept by inexperienced beginners. People only achieve the ages we do as a result of arguably un-natural conditions as well. However, I'd still be concerned if a large population only lived to be 30 years old.
If dh is degrees kH then I do wonder about the article.
After all mine live in a pH of 8.4-8.8 and kH of 4 degrees.
But then I find that "discrepancy" true on all such fish.
Perhaps some overriding factor is at work in my tanks.
like low carbon dioxide for instance. *old dude