Kitten only eats freshly opened cans of food

My new kitten (14 weeks) only likes freshly opened cans of food! I’ve tried reheating old food in the microwave but he is a fiend for fresh cans and can’t be tricked into eating food even if it’s only been open a few hours. I’ve tried lots of different foods with him and he doesn’t care what he eats as long as it’s newly opened. He needs to gain weight but I can’t be opening three or four cans a day and throwing most of it away!