Of course. You should have started let him try when he was 12months. But it is not too late
Try ask him scoop thick congee first as it is easier
Don't mind him messing the place and clothes. Ie don't show any discouragement
Delay the meal you want to train him with his spoon so that when the food finally comes. He will be hungry enough to try
Even if he just holds the spoon and uses his other methods to eat like using his fingers don't criticize. Just encourage and tell him how the spoon helps with picking up the congee
If this is still too complicated for him. Ask him to hold the spoon and you guide his hands in scooping and bringing it to the mouth