Juveniles are not physically and mentally mature compared to adults. Therefore, the Juvenile Act was enacted to protect, educate and re-socialize these juveniles. In other words, the juvenile law is based on the parent patriot. Therefore, juveniles are being dealt with juvenile crimes or juvenile delinquency through juvenile protective disposition rather than criminal punishment. However, recent juvenile crimes are indistinguishable from adult crimes. In other words, it has as much cruelty and ferocity as adult crime. Whenever these juvenile violent crimes occur, there has been an argument for a reduction in juvenile age. But juveniles are faster at reflection than adults. And it is possible to re-socialize through education. Therefore, age reduction is not the only alternative. Therefore, it is necessary to examine the relationship between the reduction of juvenile age and juvenile crime. Therefore, this paper will investigate the juvenile age of each country. Then, we will examine whether there is a common part about the juvenile age of each country. If there is no common juvenile age in each country, criminal policy measures will be devised. To this end, it is necessary to ensure the effectiveness of juvenile protective disposition. In addition, an individual educational environment for juveniles living in juvenile Detention Center should be created. Admissions to juvenile detention centers are not simply to give penal effect to juveniles. If you return to society through juvenile detention center, you have to find a job that suits you. In other words, juvenile detention centers should provide education suitable for the talents and aptitudes of juveniles. In addition, the problem of overcrowding in juvenile detention centers must also be solved. The living room should be a place where confidentiality can be guaranteed for juveniles in sensitive times. Therefore, overcrowding of juvenile detention centers should be prevented in advance.