There is theoretical and empirical support for co-offending being important not only for understanding current offending but also subsequent offending. The fundamental question iswhy? In this article, an aggregate analysis is performed that begins to answer this question. Disaggregating solo- and co-offending by single year of age (12-29 years) and crime type in a largely metropolitan dataset from British Columbia, Canada, 2002 to 2006, it is shown that the distribution of co-offences is significantly more varied than the distribution of solo offences. This more varied distribution of co-offences favors property crimes during youth but fades as offenders age. Abstract published by arrangement with Sage Journals.