Depending on how you define "juvinile". Between 4-6 months old I would feed about 4-6 small crix or mealies a day. Older than that about 5-7 medium crix every other day would do.
Really you just want to feed them as much as they will eat. Leos rarely over eat and if they do they only do it once! LOL! You also want to feed them everyday, younger leos need more food to help them grow. My little one would eat about 10 crickets a day when she was your age.
Don't leave any live crickets in there for an extended period of time. When they get hungry and don't have food they could chew at your geckos digits and are annoying to your gecko at the very least.
I'm not sure how old our gecko is, she's close to 8 inches long, we've had her for a couple of months. She eats 2-4 med/large crickets a day plus 4-6 small meal worms. We offered her a superworm yesterday but I think it freaked her out a bit--she eventually and somewhat enthusiastically bit its head off but lost interest thereafter.