I would take all of these things and put them on the tray and let him choose whether or not to put them in his mouth.
Also, I would start with larger things like fresh celery stalks as opposed to peas. That way he can hold it and gnaw it. As opposed to something so small that it rolls back and gags him.
Also, there will be a gag reflex adjustment. And it's normal and okay. Gagging is not choking. He has to figure this stuff out. Just watch and hold yourself back and help him learn to cough things up out of his gagging area.
SAHM to Magnolia May (09/10) and Luke Russett (04/13) and wife and best friend to my airman.