In our society there are two human’s versions exists, man and woman. However human beings are social animals and unlike the case of many other animals human beings can think more. Basically god created opposite sex only for breeding which is necessary for our society or nature.
Basically teenagers are more curious about this relation. The typical teenage period starts from the age of 11 for boy and 10 for girl’s case. After two or three years later they gain the ability and sense about sexual intercourse. Since in many countries the minimum marriage age are set at around 18 to 23 for both girls and boys, during this long gap their opposite sex attraction usually become in peak and they always want to make physical relation with each other before getting marriage.

There are several good reasons necessary to wait before building a physical relationship with opposite sex. The main reasons is the typical boy can fully physically and mentally developed till the ages of 21 to 25 and girl can fully physically and mentally developed till the ages of 20 to 23.
Now the question arrives that can boy and girl just be friends during teenage or young age period?
It's because of our oversexed culture. If a boy and a girl have any sort of relationship, people always assume they're sexually active. I don't agree with it, but sex is what makes the world go round these days. Everyone is obsessed with sex and no one cares about platonic relationships anymore. It's sad but true.
Some people agree that boy and girl can be friends without involving in any physical relationship and some girl trust and get along better with boy then they do girl, but some people think that they never be just friends, they must have opposite sex attraction and basically they can be engage in physical relation whenever they get a chance.
But it is also true that there are lots of field where girls and boys are working or studying together. In our society there are lots of schools- colleges are with co-education where a friendship between girl and boy is a common thing.

Some psychologist and sociologist say that this type of friendship is necessary and helpful for girls and boys both in some manners. Some girls say that their male friends are trustier and devoted than that of their female friend and in other hand boys also found that their female friends are most worthy than their male friends.
Well, I also personally think and feel that a girl and boy can be better friend for each other. The main principal is that their friendship should not intend to any physical attraction.