What's wrong with my rat?

I have a male rat, who is about 7 months old. He doesn't like to play, he doesn't jump about or get excited. I take him out of his cage almost everyday to interact with him. He'll sniff about, and that's it. Or he'll stop, and clean himself. Also, he NEVER eats out of his cage. I'll offer him a treat and he doesn't take it, or he'll ignore it. But when I put him in his cage and offer it again, he takes it right away. I'm very worried something is wrong. Please help!