Don't then! There is an increasing amount of evidence that breastfeeding longer is better, for both physical and emotional health. Both WHO and the AAP recommend breastfeeding until at least 12 months, and then beyond that as long as is mutually desired. And while it may be the norm in America for babies to be weaned by 12 months, it is not the norm worldwide! Nor is necessarily the natural age for weaning.
So nurse for as long as you want, and don't feel guilty about it.