In the countries where they are from, such as Sudan, young men may be killed to stop them rebelling against the government or used as child soldiers. In Afghanistan, young men are often primary targets for recruitment by radical groups like ISIS and the Taliban and in Eritrea they can be conscripted for what is effectively a life sentence. For all these reasons, boys as young as 13 and 14 have to run away from their homes and their families.
In Calais we see more women and children from countries such as Syria or Iran, but they are usually prioritised for social housing and not as often seen on the street.
Moreover, the journeys to Calais are incredibly harsh. From Africa they might cross the Sahara which takes many lives, then Libya, which is lawless and no woman could cross without being rapped. From the Middle East the journey is across the Balkens where nighttime temperatures can be minus 20 and the borders are rife with beatings and human rights abuses. Few women and children would survive theses horrors.