I have an innocent question. What is time? Can travelling near the speed of light make a person younger relative to others who don't? Then, is there any impact on the body (atoms, molecules etc) of the person who travels at almost light speed? If so, what is the nature of that effect?
Special Relativity tells us that time is not absolute, and different observers measure different time intervals depending on their relative motion. Time dilation is not due to an effect on the atoms or molecules that make up an observer, it is due to the geometry of spacetime.
I suggest you pick up a book on special relativity, it will answer all your questions on this topic.