better safe than sorry -- I say wait until the pooper is 16 inches or longer... You can start a supers colony, and by the time your colony gets going, I bet your dragon will be big enough to eat 'em.
http://www.beardeddragon.org/home/beardie/beardeddragon.org/forums/viewtopic.php?f=76&t=100703&hilit=
There's a ton of other options out there:
crickets - pain in the xss (stink, quick escapers, but cheap)
mealworms - too much hard outer shell, not enough good meat
(hard for poopers to digest resulting in possible impaction)
roaches - darn nice feeder (expensive on the onset, but easy to
breed, relatively slow movers, good meat to shell ratio)
phoenixworms - no experience, but from word of mouth they're
healthy for BD's but quite expensive and small
butterworms - nice treat for BD's, very fatty kinda like a
candy bar for your pooper
waxworms - don't like them. my pooper had the runs for days
after i fed a few to her. and she wouldn't eat more than 3 or 4 so i
dont think she likes em anyway