At 6 months, he doesn't need solids. They're just for fun. So, instead of using the spoon to deposit food deep in his mouth where it might make him gag or puke, how about just putting a dab of it on the front of his tongue, and treating it as a fun game instead of as an opportunity to get nutrition into him? Unless you're already doing that, in which case I think I would just put the solids away for a while longer, or maybe offer him things like whole peeled apples that allow him to hold and taste a solid without getting anything into his mouth.
Don't worry, he will get the hang of all of this! Some kids just have a super-sensitive gag reflex. But they learn to manage it.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"