Size and Length.

Question
I was wondering about the size of my pet bearded dragon. I got him a little over a month ago, from a friend. Her friend rescued the mother of him/her, and had eggs afterward. Long story short. I ended up with him when he was 4 months old and 6 days. Which was 12-16-2008.  I have had him in a 20 gal long tank. I have the proper lights, with the UVA and UVB, and what not. He gets all his supplements and vitamins. He eats his greens and crickets. (He is just now recently finally starting to get good at eating.) Before he wouldn't eat daily, even when I offered them daily. But I know people say they grow quickly. I made the mistake of not measuring him when I got him. But today he is 5 months old and 17 days. He is only 4 inches. With his tail he is 7 inches. I say he, because that is what she though the sex was. I looked at several online charts, and according to the charts, he should be at least 15 inches almost. Is there any way possible that they can grow way slower than they should? He is active, and seems healthy. He has grown a bit since I got him, but not much, he has gotten a bit wider. Thanks for taking the time to read this, and respond!

Answer
Hi Jeff,
He is very small for his age.
There are a few reasons that can  cause the slow growth and smaller size as an adult. He may be a Rankin dragon, which are smaller, but at the size he is, he would even be small for a rankin... http://www.angelfire.com/me4/pets/rankinsdragon.html has more info on them.
Poor gene pool...so many people are breeding dragons with no regard to who they are breeding to....mother to son, brother/sister..etc..over and over has ruined gene pools causing many health problems and beardies that never reach the size they should.
Please do check your uvb lights as that there are many that do not do what they say.  I am including some info I wrote on uvb and also links to reading more.
You may want to try adding some RepCal Beardie pellets to his meal...you must soak them in wam water first so they soften to about 1/2 way through.  If you don't they can dehydrate your beardie. You can also use the RepCal iguana pellets in the same manner...Be sure to feed the good greens...collards, mustard greens, turnip greens, dandelion greens, arugula... butternut squash is also fine for daily feeding. If he shows any signs of something not right, I would take him to a vet and have bloodwork done...I do recommend a fecal check now to rule out any internal parasites. The 20 gallon tank will need to be upgraded very soon,....50  gallon or larger.
I have a rescue iguana here that is very small for his age and is a very slow grower. He is a rescue, but had decent care before I took him in...and no one can figure out why he is so small at his age..he should be 4-5 ft total and hes just a few inches over 3 ft..and a lightweight!!  Health wise he's fine... sometimes its nice having one that isn't a monster in size...
LIGHTING:
BD's need UVB, which is the special lights that come in fluorescent tubes or special screw in bulbs(mercury vapor)that are designed to produce uvb and heat. The tubes do not produce heat. UVB is needed by the BD
to be able to absorb the calcium in the foods they eat. Without the uvb, they will develop metabolic bone disease.
With the tubes, they must say that they produce BOTH uvb and uva. The uvb needs to be 5% or higher. Repti Sun 5.0 and 10.0(not compact) are TWO of the best uvb tubes on the market. The repti glo 8.0's are a great uvb source also. Arcadia 5.0 (UK), which is the uvb tube available in the UK is a good uvb tube. These need to be positioned 6-8 inches(for the 5.0 and 8.0 and 8-10 inches for the 10.0) over the BD so that they get the uvb that is needed. Recommended length of the tube is 24 inches or more. They need to be replaced every 6-9 months as that they stop producing uvb long before they stop producing light.  They need to have access to uvb and basking temperatures for 10-12 hours daily.  At night, no white lights!!! There has been new studies that have proven that compact uvb lights, both the spiral/coil type and the ones that look like long "U's" laying on their side and a few other brands are causing what basically amounts to snow blindness in reptiles.  To read more on this, you can go to
http://www.uvguide.co.uk/index.htm  Here is a link to a letter from RZilla on their product: http://www.zilla-rules.com/assets/006/13278.pdf
There are tubes and bulbs that say ''full spectrum'' but they do not produce any uvb.
On the mercury vapor , they also produce heat. They also produce the uvb and uva. The best on the market now are the
MEGA RAY or the T-Rex.  www.reptileuv.com has more information on the Mega Ray lights. When using these, the distance is much greater than the uvb tubes and the directions must be followed that are listed for the light. When using the mercury vapor lights, you don't need to have one light for uvb and one for heat. The Mercury vapor lights provide both.