There are numerous reasons why a guy would want to make out with a girl. For some, especially during puberty, they are being controlled by their hormones and therefore the urges are at their peak. For others, they may want to express how they feel about the girl by making out with her. It good to wait until you are mature and very sure of what is good for you before doing it.
Because of puberty, hormones, and testosterone they are more sexually active than girls...girls have very little testosterone but some girls become sexually active early depending on their surroundings or peer pressure