Nothing in Section 91-7-209 shall hinder the application of the doctrine of estoppel to assert title to adult heirs who received a share of the purchase-money of land as heretofore announced and applied in this state. The same rule may be applied to minors, persons of unsound mind, convicts of felony, and other wards whose guardians received for them a share of the purchase-money, whether it were actually applied to the benefit of or received by such person under disability or not.