Goldfish can live anywhere from 15-30 years when properly taken care of and koi can live as long as 50 years and reach lengths of 3' with good care and genetics. The key is in knowing how to properly take care of them...which most people don't. For starters, they're not tank fish, they need about 500 gallons apiece to reach their full potential, which is why they're very popular for large ponds. I will get started on a hub on this subject that goes into more detail, but there are also some good resources at http://www.kokosgoldfish.com. Definitely be very careful where you get information on their care, there is more misinformation on the internet about goldfish and koi than on just about any other type of fish.