year变成years：前面是14,用名词的复数
go变成goes：主语是他,动词第三人称单数
in the morning变成on the morning：介词搭配,如果中间有修饰语才能用on
come变成comes：第三人称单数
study变成studies：第三人称单数
He not do many homework.变成He doesn't do much homework.否定词在助动词后,homework不可数,用much
good变成well：修饰动词,词性是副词
plays变成play：前有情态动词,则一般动词为原型,不加s
这段话应该改成：
Tom Smith is fourteen years old.He is in Grade 2.He goes to school at eight in the morning,and comes back home at half past three.He studies English,math and other subjects.He doesn't do much homework.He swims very well and he can play football.