They also start to eat less as they mature.
As a baby, my boy would finish an entire bowl of food in one night. Now, he'll only eat about half that bowl.
But we would need more background information before anyone can really make any suggestions.
As stated above, how many kibbles, has he lost weight.
Has anything changed? Lighting, heat, environment. What is the temperature at?
How old is your hedgehog?
Some older hedgehogs eventually need help with their food, whether it be crushing, or soaking so that it becomes soft.