There is no legal provision preventing a minor from traveling alone. However, minors traveling alone remain under the responsibility of their parents, and therefore they have to judge whether their child can make the journey alone taking into account the possible dangers of travelling alone.
For air travel, it will depends on the airline. Children can travel alone and will be usually taken care of by the airline. However, the age from which the child can travel alone accompanied by a staff member and the age from which he can travel alone without being taken care of by the staff of the company varies.