M.P.
When I was a first time mom I worried about all that stuff too. Now, a mother of 2, (3 & 15m) you realize that babies don't need to be as complicated as we make them.
Here is the one thing I have learned along the way...babies will let you know when they are ready for something and when they are not...no matter what it may be. If he's gagging then wait. If you want to give it a try in another few weeks, go for it...if he still gags, he's not ready. Don't fear developmental delays....every baby is very different. My daughter did everything 3 months earlier than the books say kids should, and my son is doing everything 3 months later than the books say he should. He personality is so laid back and she has always been so very eager to do and learn new things. It's just the kid.