How can I prevent this model to learn more(less) :)))
Well, by making your model better, I suppose you mean enforcing some sort of regularization on it, so that it doesn't overfit. Early stopping, however can be viewed as a regularization method by itself. 

I would suggest sampling the performance of your model more frequently (than the 200 examples you are doing currently) and if you see the validation score is not improving after a few iterations stop the training.

Early stopping can be implemented through the monitor parameter in the GradientBoostingClassifier's .fit() method.