By now he should be eating foods like rice, pasta, meesua etc etc.. In short, any kinds of foods that we eat.. My son has started rice at 11mth old and baby pasta at avout 9mth old. He still prefer porridge so we just cook for him but no longer 'baby' porridge.
I think it is time to introduce him thicker texture. Maybe he is just now used to it, after all he have been eating baby porridge for so all. If he dont wanna eat, dont force him but let him know it is time for him to eat thicker texture and hopefully he will understand soon. Or you can try to let him have some plain rice and see if he likes it? Some kids only eats baby porridge but they will like rice cos it is a different thing for them.