is my baby behind

So my son is 1 since May 30th. He doesn't crawl. Doesn't walk. Will sit if I sit him down but otherwise won't even try to pick himself up. I know he's not weak. He is being lazy. If I put him in the walker he follows me around. Also WIC now said I have to start him on food. He eats gerber ok. But every time I introduce food he gags and pushes me away and wants nothing to do with it. How can I get him to eat FOOD FOOD. ?  He is breastfed and also prefers that over anything. I notice it's not enough to fill him anymore.