The issuing officials shall provide for the amortization of debt represented by college savings bonds over the term of the bonds as prescribed by the Constitution for debt to be amortized in substantial and regular amounts. The first amortization shall be due prior to the expiration of a period equal to one-tenth of the term of the debt. For the purposes of this chapter, bonds are amortized in substantial and regular amounts if they mature annually or semiannually and the largest initial principal amount scheduled to mature in any one bond year does not exceed an amount equal to three times the average of the annual initial principal amounts for all other bond years of the college savings bond issue. Within the limits imposed by the Constitution and this chapter, the issuing officials shall establish periodic maturity amounts so as to reasonably meet anticipated demand by individual investors for the various maturities, but in no case shall a college savings bond have a maturity date greater than 20 years following the date of original issue.