how old is my Zebra finch

Question
Hello. Yesterday my daughter purchased 2 Zebra finches. She
bought them without asking some questions that i hope you
may answer for me. How can i tell how old these finches
are?I think from the bright colors of one that he is a male
and the other a female. The bright colourd one seems to
have no feathers around his bottom, is this because he is young, or might he have some sort of mites?Is there
anything special we should be doing? She would like to
breed these birds but I'm not sure of the health or age.Any
further info would be helpful. Thank you

Answer
My advice to you first off is to buy a book about zebra finches. This will help you a lot more than I ever could. This will also be very useful if you do decide to breed them.
All birds have a little band around their foot that will indicate the year they were born in (http://www.friskyfinches.com/banded%20baby%20gould.jpg the band will be similar to that). Zebras have a pretty easy way to tell which one is a boy and which one is a girl. Boys USUALLY (not always) have orange cheek patches on their face after they get their adult feathers in. Girls don't have this. Another way to tell is by blowing on their butt. A male will have long "feeler feathers" around the rim whereas females are completely bare of feathers around that area. The best way to tell though is to simply get them sexed by a vet.
I recommend that all finches bought from a bet store should be brought to a qualified avian vet to checked over just to make sure that everything is alright with them and to get them treatment early on if something is wrong. The most common thing for store bought finches to have is air sac mites. These little mites will get into the bird's throat and lungs and keep multiplying until the bird is dead (suffocation). You can detect them at home a few different ways:
1 drench the birds neck and shine a powerful light through it (be careful though, their necks are very fragile). If something is there that shouldn't be, you will know.
2 hold the bird up to your ear and listen to it breathe, if it is clicking, chances are it has air sac mites
3 Open the bird's beak (best way is with a toothpick where the ends have been filed off) and look inside the mouth. If it's black where it should be pink, it has air sac mites.
4 smear the bird poop on a white sheet of paper (or tissue, your choice)and see if it has a grainy look to it. Air sac mites infect other birds through bird poop, sharing food, and water
5 give your bird a couple drops of water, it is starts gasping at a small amount, it has air sac mites.
After determining that the bird has air sac mites the vet will more than likely prescribe something called Ivamech (doubt that's the way it's spelt but that's how it sounds). This is something used to treat livestock. It's too powerful for finches and has been known to kill them. It's better to get something called Scatt. It's like Ivamech but a much milder form; making it perfect for finches (I think the other name for scatt is Ivamechtin but I'm not sure). For any more questions on bird health, please ask your bird vet. They would know more and the more you know, the better off your finches will be