Whenever in any action it is material to any party to show that the title to any tract of land is vested in any county, under chapter 132 of the general laws of 1866, by having been bid in for such county for 5 successive years on sales for taxes and that the tract remains unredeemed, the statement of such sales made by the county treasurer, or the record of such statement in the book kept for that purpose in the treasurer’s office, or the certificates of such sales executed by the treasurer to the county shall be prima facie evidence of the regularity of the tax proceedings from and including the valuation of any such tract of land up to and inclusive of the sale thereof and of the existence of all conditions precedent in any way affecting the validity of such sales, or requisite to make the title of such land absolutely vest in the county in which the same is situate. This section does not apply to any such lands if it appears that they were owned at the time of the sales by minors or individuals who were adjudicated incompetent or mentally ill or were under guardianship.