Whenever it appears to the satisfaction of the agency that a guaranteed loan made in accordance with the provisions of this chapter is in default, and the eligible lender has certified such fact to the agency, the agency shall reimburse the eligible lender making the loan from the reserve fund to the extent the loan was guaranteed by the fund. Whenever payment of the guaranteed principal balance of any insured or guaranteed loan is demanded of the agency, the note and accompanying evidence of the loan must be tendered to the agency in manner and form to confer good title so that the loan may be collected by the agency as it may determine according to law. Neither minority nor any statute of limitations may be used as a defense against collection of any loan through court proceedings.