I am 19 years old and i would like to get rid of my genetic double chin, in fact i would like just to define jawline. is there any method to do this?

Yes: It seems that you need something like a "neck lift/face lift". Because you are young this may be more surgery than expected. See a board certified plastic surgeon for a consultation.

Chin implant/lipo: If you have a full neck from fat accumulation, you most likely have a weak chin projection. By having liposuction to remove the fat and a chin implant to increase the projection, you can redefine your jaw line and create a pleasing neck contour.