Actual occupation for three years, after two years from the day of sale of land held under a conveyance by a tax collector in pursuance of a sale for taxes, shall bar any suit to recover such land or assail such title because of any defect in the sale of the land for taxes, or in any precedent step to the sale, saving to minors and persons of unsound mind the right to bring suit within such time, after the removal of their disabilities, and upon the same terms as is provided for the redemption of land by such persons.