I'm sorry your beardie is stunted, a photo of him would help, but he should be much larger than you're describing. To give you a comparison, my female is 7 months old, almost 8 months old, and she is just under 18 inches long from the tip of her snout to the end of her tail. At 6 months I'd say she was probably between 16-17 inches long. Now all Beardies are going to be different, but 7 inches long from end to end is way too small for a 6 month old, and as you've stated he hasn't grown much since you got him, so something is very wrong to stunt his growth this much.
We need you to post photos of him, as well as photos of his enclosure and setup. His daily diet is only one part of why his growth is stunted, there are a ton of factors that effect a Bearded Dragon's growth and development, including diet, UVB exposure, temperatures in his enclosure, dietary supplements, etc. So we need to know everything about his enclosure and setup in order to correct this problem and get him on track, because he is way behind and not only will he probably not grow to his full potential even with the corrections, but he's going to most likely develop a lot of other issues that are debilitating and possibly fatal, like Metabolic Bone Disease.
A good rule for feeding your bearded dragon is to let him eat as many live insects, crickets in your case, which are good feeders (I hope you're gut-loading them with good greens) as he can eat in a 10 minute period, and you need to do this twice a day at the least, 3 times a day is better. Unfortunately you didn't do this when he was a young baby, and that's when he needs adequate nutrition the most to grow. For example, my girl was a little over a month old when I got her and around 5 inches long at 2 months old. I would feed her in the morning after her lights had been on for at least an hour (important) and in 10 minutes she would eat between 15-20 small crickets. Then I'd feed her again around 4:00 when I got home, and again in 10 minutes she would eat between 15-20 small crickets. Then I'd feed her again about 2 hours before her lights were turned off (important because they need their
UVB light and heat from their basking bulbs to digest the food). Again, in 10 minutes she would eat between 10-15 small crickets. So on average at 2 months old she ate between 45-60 small crickets a day. There should be no set number that you're thinking of feeding your beardie, it's simply as many crickets as he can eat in 10 minutes, 2-3 times a day. Some eat more, some eat less, but for a young, growing beardie 15 small crickets a day is not nearly enough. And you should have been dusting ALL of his crickets in Calcium powder 5 days a week from the time you got him until he is at least a year old, and the other 2 times a week ALL of his crickets should be dusted in a good reptile multivitamin powder, again this should have happened twice a week (Calcium powder off days) from the time you got him until he's at least a year old. So a lack of Calcium may have caused the start of Metabolic Bone Disease, and the total lack of a multivitamin powder obviously has effected his growth and overall health.
As far as fresh veggies, most babies won't eat them, some won't touch them, some nibble on them, and some really do love them. As they approach a year old they make a switch from 80% live insects and 20% veggies to 80% veggies and 20% live insects. However, they should still be provided fresh greens and veggies every single day so that they can learn to eat them, and if they do it's a bonus because they are loaded with important and necessary vitamins and minerals, like Calcium. Now feeding your beardie shredded carrots every day was not appropriate at all, carrots can be added to their greens once in a while if he likes them, but they need to be given fresh greens every single day that are rich in USABLE Calcium! NO LETTUCE OF ANY KIND! Lettuce, even romaine, has very little to no nutritional value and is mostly just water. NO KALE OR SPINACH!!! These two are loaded with calcium but also loaded with oxalates which bind the calcium and make it unusable.
So you should be offering fresh collard greens, mustard greens, Dandelion Greens, turnip greens, escarole, bok choy, cilantro or basil (just a little for flavor), green beans, sugar snap peas, squash such as butternut or spaghetti (they usually love squash), sweet potatoes, broccoli (in moderation)...Those are the best ones, with the best listed first, like the collard greens, mustard greens, Dandelion Greens, and turnip greens. There is a really great list of veggies and greens on here if you search. Make sure to buy fresh, not frozen, and NEVER CANNED, there are no nutrients left in canned veggies and they are loaded with salt and preservatives that are horrible. Again, you could add shredded carrots to the greens if he likes them, it may encourage him to eat the greens, but carrots cannot be a staple veggie. Fruits are just sugar and water, they cause runny poop and have little nutritional value, so only give them once or twice a week, if that, and in small bits. Make sure you rip the greens into small pieces that he can fit into his mouth.
You're going to have to start over with his diet from this point on, forget about him being a year old and switching off of live insects because he's going to need the protein from this point on just like when he was a baby, since he didn't get it then. So prepare to feed him 60 small crickets a day (I need a pic to see his head size, I'm assuming he can't or should not be eating medium crickets yet, they can be no wider than the space between his eyes). Prepare to feed him fresh greens and veggies every day (I put the greens in after I do her morning 10 minute feed so she has them from the morning feed until I get home around 4:00). Please also go buy a quality Reptile Multivitamin Powder, like Repashy Calcium Plus or Herpavite. He will need that dusted on his insects twice a week, and the calcium powder with D3 5 times a week.
Now, the second part of the problem is no doubt his enclosure and lighting. Again, please post a photo of his entire enclosure and setup, including the lights.
Then please answer these questions, as they are very important. Please make sure to list brand names of your bulbs, along with the model and the wattage (all will be listed on the bulbs themselves if you don't have the boxes). If his lights are inappropriate he can't process any of the calcium, multivitamins, or nutrition from the crickets or veggies, which is the other half of the reason he is stunted, I'm assuming even though I don't yet know what lights you have. Do answer these questions as accurately as you can, as well as posting photos of him and the enclosure, and we'll know exactly what's going on:
How large is his enclosure/dimensions? Is it a glass aquarium or a reptile specific enclosure? What substrate do you have in the bottom of his enclosure?
What brand, model, and wattage/size of
UVB bulb do you have? Is it a long, flourescent tube, a regular lightbulb, or a coil light bulb? How far away (in inches) is the
UVB light from his main basking spot? Is the
UVB light mounted inside his enclosure or is it on top of a mesh or glass lid?
What brand, model, color, and wattage of basking bulb do you have? How far away from his basking spot is the basking bulb? Where is it mounted, and how close can he get to it? Do you use any type of colored bulbs or a Ceramic Heat Emitter (CHE) for nighttime?
What are the 3 important temperatures inside of his enclosure: Hot Side Temperature, Cool Side Temperature, and Main Basking Spot Temperature? What type of thermometer did you use to measure those temperatures? How many hours per day are his UVB and basking lights on?
We already know about his diet and supplements and I've already informed you of what changes you need to make immediately to that. As I said, his daily diet and supplements are only 50% of the issue, so even if you change to feeding him as many crickets as he can eat in a 10 minute period 2-3 times a day, and you ditch the carrots and start feeding him appropriate, fresh greens every day, and you start dusting all of his crickets in calcium with D3 powder 5 times a week and a Reptile Multivitamin Powder the other 2 days a week, none of this will do much good if his lighting and temperatures are wrong. Bearded dragons have very unique and specific lighting requirements, specifically their
UVB light requirements are very, very particular, and unfortunately most UVB bulbs that are great for other reptiles absolutely suck for bearded dragons, and most pet store employees and as we're recently finding out a lot of breeders don't have a clue about proper UVB lighting. So you definitely need to get on this immediately, correct his diet, and as soon as you answer the above questions we can tell you what's going on with your lights.
Please try to get him turned around ASAP because he is extremely stunted and most likely has some health issues.