Basically the rule of thumb is to let the lil guy as many as it can in 10-15 minutes. Make sure the crickets are no bigger than the space between its eyes.
normally a young beardie like that should be eating around 50-100 crickets a day, but anything can affect its appetite. If he/she is shedding, then it might not eat as much until the shed is all gone, if you just recently got the beardie, he/she may be going through relocation stress and it is perfectly normal for them to eat very little or nothing at all at first. One of the bad signs of a poor appetite is that it might have parasites or other health problems.
Just be sure that you offer it a good amount of crickets, even though he wont eat it all. Give it a couple days, if the its appetite is still poor consider taking a fecal sample to the vet.
Also make sure your temperatures are all correct, 105-110 in the basking spot, and 80-85 on the cool end.