S.
He is old enough to feed himself. My 9 month old eats pretty much everything we eat. She does have teeth already so that makes it easier. Maybe you want to start giving him some cut up banana, whole milk cottage cheese, cut up cheese, rice, pasta to start. Make it high calorie foods if you are concerned about his weight. Maybe he is bored with jars.
They do go through stages where they may not eat as much. And he may be teething. As long as you still breast feed he will be fine.