how to find the age of the gold fishes?

Answer 1

If you just asked a question on how to tell the age of a fish and all the answers say you can't then one would think that you can't tell the age of a goldfish either.

Answer 2

sweetie there is no way to tell the exact age of a gold fish :(

Answer 3

"It is nearly impossible to sex a Goldfish accurately under the age of 1.5 - 2 years of age, even then it is quite a task".
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Goldfish 101
Introduction: Goldfish are perhaps the longest kept "aquarium" fish in the hobby. They’ve been kept for several thousand years. With such a long history you'd think they would have morphed into this superfish that doesn’t require its keeper to do anything, right? WRONG! True Golds are quite hardy and do endure much abuse, but they are still a living, breathing creature that has certain requirements that must be met in order for it to be kept as a real pet and not a discardable piece of decoration. This article should give you an idea of what are these requirements are, so you can decide it Goldfish are for you or not.
The Basics: The biggest and often times most fatal misconception of the entire aquarium hobby is the "fish bowl". Now what fish could honestly be suited to live his life in such a ridiculously small space? Well a Betta might handle it, but a Goldfish certainly does not. Little Goldfish who are stuffed into these things never get past their "childhood", living a sad, short life. I have heard many times of owners bragging "I kept *my* goldfish alive for 6 months in its bowl", this is truly funny and sad at the same time, since these people have no idea that goldfish live to be well over 10 years in tanks of at least decent size, and are known to actually live 20 years or more! The reality is: Goldfish are large, messy, oxygen-hungry fish that produce a ton of waste. This is why it cannot live in that bowl for a long time, even if daily water changes are made.
Tanks: An appropriate sized tank will be needed to house goldfish. I suggest you start with a minimum of 100 liters, this size tank can house a pair of fancy goldfish quite comfortably for quite some time. Generally, a tank of greater surface area is better than one of lesser surface area, so a hexagon or pentagon type tank is not the greatest format for goldfish.
Filtration: You will need a hefty bio filter as well as an extremely efficient mechanical filter to handle even a lightly populated goldfish tank. In my opinion it is best to use 2 filters, 1 dedicated to bio filtration the other dedicated to mechanical filtration. A turnover of around 10-12 times the tank volume per hour is good. Do keep the water level up so that too much current isn’t made, since fancy goldfish are slow moving fish that don’t have the easiest time in the world getting around anyway. You will probably find yourself replacing the mechanical media often, I have found floss to do the best job at this. I don’t personally recommend under gravel filters (UGF's) since goldfish are always digging around in the gravel and do produce some high waste loads, but a reverse flow UGF would probably do OK.
Décor: This really is an optional and personal preference thing, but some décor does make the fish feel safer and therefore reduces stress. Despite popular belief, fish in general don’t care if it's glow in the dark gravel and PVC pipes or a lavishly planted tank, they don’t know the difference. However, most fancy variety goldfish do have certain limitations in the décor you choose. Don’t use anything sharp that they (especially the bubble eyed types) can injure themselves on. Use small gravel, I nearly lost a goldfish due to a piece of gravel becoming stuck in its mouth. It was no simple task getting it out. Small gravel or sand is also much easier to keep clean than large gravel as the food and waste stays closer to the top. Goldfish do like live plants, and they do benefit from the constant availability of vegetation, but they will eat most plants. So you may not want to invest in a 10 dollar a plant like a Madagascar Lace or so forth. I use Hornwort, Elodea, Java Moss, Java Ferns and Anubias Nana. They don’t eat these last three plants, but they do eat the cheap, an-inch-an-hour growing Hornwort and Elodea.
Diet: Golds in general are omnivorous, meaning that they will eat plant matter as well as animal matter. However, Golds must have some vegetation in their diet, to prevent certain digestive problems. This can be easily provided by some live plants (as mentioned above), as well as by feeding the fish chopped lettuce, chopped spinach and deshelled peas. A good quality commercial goldfish food or two should be the "staple" of the diet, with the feedings of lettuce, spinach, peas, etc as a treat. I always skip at least 1 day of feeding per week on Goldfish as this "cleans them out" internally, which is good for them. Soak all foods prior to feeding, as this lets the food instantly sink so the fish doesn’t get that big gulp of air while feeding. That can actually prevent some swim bladder problems, which they often have. Feeding lightly helps too.
Sexing: Golds are difficult to sex. Although it *is* possible. The best and most accurate way, in my opinion, is the tubercules that develop on the gill plates of the mature male. They appear to be tiny white spots, you probably won't even notice them without close examination of the fish. Females also are usually a big larger fuller bodied. It is nearly impossible to sex a Goldfish accurately under the age of 1.5 - 2 years of age, even then it is quite a task.
General Maintance: You will probably find yourself doing some hefty maintance on a gold tank. I recommend at least a 25% weekly water change, twice weekly of 20% is much better. Your tank may even need more water changes to remain stable. You should rinse the mechanical media twice per week and change it at least every 2 weeks. Bio media should be rinsed at least every 2-3 weeks. Vacuuming the gravel at least weekly helps as well.
Tankmates: Typically goldfish do best in a species only tank. Although it is quite possible to keep other fish with them. But you must be careful in the fish that you choose. They must be placid enough, have similar water requirements and be able to handle the lower temps (18-25°C) enjoyed by goldfish. I have had mounds of success with Zebra Danios, they are relatively close relatives, and do have a lot of the same requirements as goldfish. Apple snails are marvelous algae eaters for the goldfish tank. White Clouds would probably do OK in a gold tank as well. I wouldn’t put any of the more strictly "tropical" fish like tetras, and definitely not any cichlids.
Conclusion: Goldfish aren’t hard to keep, provided their owners are ready to provide them what they need and aren’t afraid of a little work. They are very rewarding, personable family pets, grow large and beautiful, and live many many years.

Answer 4

cut one in half and count the rings