Hi M.,
My daughter is 7.5 months old. I started her on soft cooked vegetables at about 6 months. She does fine. If he is exhibiting signs of 'chewing' ... then he is most likely ready to have some table foods. When they can mimick chewing then they are developing the skill to move food to the back of their mouths and swallow it.
Their gums and masticate soft cooked veggies and things that dissolve easily (like O cereal) and they have no problem swallowing it.
Honestly, the best way to give soft cooked veggies is to cut them into sticks... like thick french fries. They can easily manipulate food with a handle. At this age they often aren't capable of realizing that what is hidden in their fist can be eaten as well... so chunks that are too small, they won't eat well. Also, not all babies have the pincer grasp mastered at this age. So, stick shape is best. Of course offering something like O cereal does encourage that pincer grasp.
My daughter eats celery, broccolli, carrots, parsnip, apple, and pear. This week we will introduce zuchini. She loves to eat what we're eating. It's SO fun!
If you want to look up more info on this... google 'Baby Led Weaning'. There isn't alot of info out there on it... but there is some.