Any dog owners out there can help?

Renji is about 7 months old, I feed him 3x a day a little more than 1/2 cup of dry food each time, exactly what the measurement on the bag says to feed him. yet when he eats he eats like he's never eaten before, like he is starving, famished, on the verge of death. he inhales his food in less than 30 seconds. I've tried feeding him less food, more often, but he still eats like it's his first meal in weeks. Is it okay to just let him eat like that? should i try to correct it? if so how? It's like he is always hungry.