How Old Til I Can Feed A Kitten Hard Foods??

My kitten is 4 weeks old (I bought him at 2 1/2wks), he has been eating real mushy food since the day I found him. He’s not acting like a kitten…he’s still very active, climbs on me constantly and eats fast….but today when my husband gave him his first taste of Solid Gold (chicken flavor) he threw it back up within 10 mins. Does this mean that even though I fed him hard foods, he is too young to eat solid foods? Is there a way for me to make sure that what ever food goes in his mouth will stay in his stomach?? Any help would be appreciated!! Thanks!