I need to know what's an extremely healthy diet for most 19 year old guys?

Paleolithic. If health conscious, he may like the paleolithic diet (see thepaleodiet.Com) avoiding processed foods and sugar. This is good for everyone. Other components are more controversial but I have found very helpful in practice. You will usually not be successful in getting a reluctant family member to change eating habits unless you 1) eat the diet you recommend 2) stop buying the processed foods.