It is recommended that mothers breast feed an infant for at least 12 months. The breast milk is much healthier for the child as it changes over time to meet the infantsilds nutritional requirements, is much easier on the digestive system, and confers immunological resistance.
As far as what is too long, I cannot say. However, I find it interesting that in many cultures mothers breast feed children until the age of 3 years an more and these kids do not have "issues". After all, the pupose of a breast is to nourish a child, not to fuel some greasy teenager's spank fantasies.
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