Is it all right if a 13 year old boy stalks a 13 year old girl if he has a crush on her?

No, it is not acceptable for anyone, regardless of age, to stalk another person. Stalking behavior can make the other person feel uncomfortable, unsafe, and violated. It's important for individuals to express their feelings in healthy and respectful ways, and to respect others' boundaries. If someone has a crush, they should seek to communicate openly and respectfully rather than resorting to stalking behavior.