Yes it is true, Goldfish can live 10 to 15 years or more, I think one of the oldest goldfish was around 44!
Floating pellets will be fine and goldfish will always act hungry
There are other foods you can feed them, such as freeze dried and frozen products which come in a variety of flavours such as tubifex worms, blood worms, daphnia, krill, shrimp etc. You can also feed goldfish some fruits and vegetables, but quite often it's down to their personal tastes as to which ones they'll eat!
We have a thread here on the forums, which is a guide to feeding vegetables - (Link is not visible to guests. Please register to view.
While I can appreciate your goldfish are only around 2 inches at the moment, they will need a larger aquarium soon. As I mentioned previously my goldfish Lucky grew an inch in just 3 months!
One of the main reasons it is recommended to have 10 gallons per fish, is not only because of the growth, but also because of the amount of waste goldfish produce, so the more water they have, the better as it makes the waste less concentrated and less harmful to the fish. Otherwise if the tank space is too small and/or the tank has too many fish, the water will become toxic and will either make the fish very ill or kill them.
Actually that's just made me realise, did you cycle your tank?
When a tank cycles, it goes through the nitrogen cycle (there are several threads around here that explain it very well, so I'll just do a brief summary).
So to begin with Ammonia levels will rise and spike, bacteria will be developing which transform Ammonia into Nitrites, then Ammonia levels will go down and Nitrites will spike up, then more bacteria will develop turning Nitrites into Nitrates.
Ammonia is deadly to fish and Nitrites are pretty bad for them as well, but Nitrates are okay in a low concentration.
So as fish keepers, we either have a water testing kit at home or we take our water sample to a local pet shop.
This will then tell us what the Ammonia, Nitrite and Nitrate levels are in the tank. So in a fully cycled tank Ammonia will be 0ppm, Nitrite will be 0ppm and Nitrates will ideally be below 40ppm (ppm stands for parts per million, it's how things are measured in aquaria).
With the photos, I believe your log ornament is like an air stone? So am I right in thinking you currently don't have a filter? How often are you doing water changes at the moment and when you do a water change, do you use a water conditioner?