How long does it take for boys to mature?

This varies on the person you are talking about.

It may be when you are 8, or when you are 20.

Usually You'd Mature around 13 - 16.

Maturity is not a simply physical change in the body. It is an attitude, an awareness of how things are and not how we would like them to be.

That happens (and in some cases does not) at various stages in our lives. Nor is it just a male phenomena. Some boys never 'grow up'. Neither do some girls.