What can be done to grow taller naturally, i am 18 years old ?

Adult height: If the growth plate in your bones have closed, you will not grow any taller. Most 18 year olds have stopped growing, but some will grow a bit more, especially boys. There is not much you can do, except eat well, be healthy.

Nothing specific: Keep active ; a healthy diet but don't expect to grow taller.At 18 most males growth centers have closed making increased height unlikely.If you want to know for sure an x-ray of your wrist ; hand can be analysed for bone maturity ; tell if the growth centers remain open to new growth.