Maturity comes with knowledge and other things that you learn during your life (from experience and other sources). So a person might not be considered mature at the age of 14 but they could be more mature than a adult at the age of 18, because they experienced more difficult situations or things like that.
Normally its the pleasure of doing so or they are just in need of something (i.e. robbing a bank-in need of money). Most people who do something wrong to get something they want do it for the thrill or the pleasure.
