The age of consent is a tricky question because different cultures will see it much differently than others. In terms of biology, an individual is fertile and ready for reproduction during puberty, but this can occur at a very early age. The problem is that individuals do not fully develop mentally until much later, and it becomes an ethical issue.
The US as a historically religious nation has a very stringent 18 year old age of consent with some states being 16. In many countries of Europe, the age is as low as 14 and the same goes for many middle eastern countries that have it lower. Regardless of legality, it is seen as quite shady in western nations if an older individual seeks out much younger individuals.