Hi,
I also have a micro-beardie. Kazul is about 3 months old (give or take) and just barely 7 inches. From poking around the forums, here's what I've gathered...
1. Poor husbandry mistakes in the very beginning can stunt their growth. After buying Kazul - super tiny then - at a pet store (never again), I spent most of the summer fixing the lighting, food, etc. Now I'm hoping he will catch up. Even if he doesn't, though, he should still be healthy - just smaller. Did your baby always have the setup you described, or were there things you changed in the beginning?
2. Accurate temperatures are super important. The temps you listed look good, but how are you measuring them? I thought my temps were right until I bought a temp-gun to double check. After I adjusted, Kazul started eating even more.
3. Parasites can stunt growth. Typically you'd know you had a parasite problem because his poop would be REALLY smelly and he would seem malnourished, not just small....but it's worth checking out just to know for sure.
4. I ordered ParaZAP online because I wasn't convinced Kazul had a parasite problem and couldn't afford a vet trip. It's *supposed* to stimulate appetite and growth by lowering parasite counts naturally. I am not convinced of its effectiveness, but it couldn't hurt to try.
5. Are you sure your dragon is 100% beardie and not partially Lawson's?
Our beardies are small, but in the end, beardies don't ALL grow into giants. Some, despite clean bills of health, normal eating habits, and proper husbandry, still only get to maybe 12 inches or so. They're called "micro-beardies" here. You and I both, I think, are in the phase where we double-check that we're doing everything right, cross our fingers for a growth spurt, and accept the outcome that a healthy dragon can still be kinda small - as long as it's healthy. I hope other people respond here with advice that we can both take!