Iam 21 and 6 months old, i want more height can strecthing exercises would work for me. if i do strecthing exercises daily (for an year) ?

No longer possible: Bone growth occurs at a part of the bone called the growth plate (near the ends of the bones). The growth plates "close" (basically disappear) in men between the ages of 18-21. After that time there is no way to grow taller. Our height is mostly determined by our genes. Measures to naturally increase growth hormone may have helped you a bit a few years ago, but at this point you are full-grown.