In the April-June 2010 journal of Sexual Addiction and Compulsivity, a study conducted by Sandra S. Stroebel from the Department of School Psychology Marshall University centered around boys inserting objects into their rectum or urethras during masturbation before age 18 and the effect this had on their sexual habits later in life. 

The study used data provided by 841 men using an anonymous computerized survey.  The study found that the boys who engaged in this kind of activity prior to 18 years old were approximately 15% more likely to insert objects into their rectums and/or urethras into adulthood.  It also increased the likelihood of them wanting to use objects in relation to their partner’s genitals and/or anus.

These results are not surprising since we know that many habits as well as likes/dislikes (including sexual ones) can have their roots in childhood.