Generally these things should be discussed as they enter adolescence. The word sex should be replaced by attraction between boy and girl and how its purpose is to have children after marriage. Adolescents need to understand the difference between physical attraction, emotional feelings towards someone and true love. All this can be explained in a simple matter of fact way without stressing the point too much or excess emphasis
Especially boys should learn that love implies care, affection, sharing and giving rather than simply a physical attraction.
Affectionately,
Alok da
