*Hey Megalofyia!* Plese don't take offense at this post!
It's not meant to be rude!
What literature states this? Internet sites, books, scientific journals? Did you read this at http://www.fishpondinfo.com/neon.htm
I've read more like 3-4 years max in a couple of books. I'll check on that, though. Petsmart.com has "The Neon Tetra has a ten year average life span" written on their page. What a ridiculous thing to state, though. By whose standards of average? If you averaged all aquarium-dwelling NTs, you'd probably get an average life of 4 days. If you averaged lives in the wild, you'd probably get a few hours or a day (most eggs or fry eaten immediately...). Well, sorry. The wording is just pretty poorly thought-out!
I'd love it if they do have such a lifespan--much more time to enjoy them! It's hard to believe, though!
If I remember, I'll read up on this...
As for me, I've only kept mine for a few months, but they're going strong! 8)