I think it's too much as a general rule, but in individual cases it might be just fine. Certainly, if his parents want him to learn Chinese, now is the time to begin—if not sooner. In Singapore—a country that is officially bilingual—children from Chinese-speaking homes learn English in early childhood programs, while children from English-speaking homes attend Chinese language programs. If the school is attuned to the needs of young children, an intensive bilingual program with heavy emphasis on pre-academic skills does not need to be stressful. However, it certainly can be. I would say that the little boy's behavior is the best indicator as to whether this is too much for him. If he whines and cries and doesn't want to go, I would say it's too much.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.