How old can an aquarium fish get?

[choochoo]

for example neon fish or guppies

[tikitiki]

Depends on the type of fish....oscars and large cichlids like that over 10 years, goldfish 10-20+ years, smaller fish like guppies and neons probably average about 1-3 years. I have some large cichlids and some goldies going on the 8 year mark, and a few cory cats going on the 6 year mark. Lots of other factors involved as well, like proper care and upkeep of the tank, varied diets, etc. can all help them live longer.

[mr. Deneau]

small fish can live to about 5-10 in really good conditions it also depends on the fish's sensitivity and how susceptible they are to disease and parasites

[Paul]

neons will live for about 5 years and guppies about 3 years i would say the average is about four years although livebearers live only about 2 or 3 years or killifish live only one year but larger fish like cichlids and goldfish can live for about 20 years

[reallypablo]

Neons and guppies only a few years.
I remember reading about a scientist who brought back a species of upside-down catfish from the wild, and it lived over 50 years. I can't find the article where I read that, but here is a link saying they live 15+ years:
http://www.aquariumlife.net/profiles/african-catfish/upsidedown-catfish/100059.asp

Check out this link for the 20 most popular aquarium fish and their average life expectancies:
http://www.stripersonline.com/surftalk/showthread.php?t=433815

[Veronica Alicia]

Corydoras seem to be able to go on for 20 years - I've a couple of "Pepperpots" who have outlived everything else I've ever had.

[expert of some stuff(read what)]

in exellent conditions maybe 5-10 years, but this only happens in massive species only tanks with pristine water and perfect everything.