My 18 months old still can't chew chunkier food without gagging .. is this normal ?

Normal, especially when they're not used to the texture. Just keep giving them the same food so they get used to it. But try to make the chunks smaller and gradually up to their normal chunk size consistency

it's normal. depends on how long you started feeding your child. i started my boy early so till date so far so good for me.

It's normal. some kids take a longer time to adapt on chunky food texture