(1) Notwithstanding section 81, a member may retire with a retirement allowance computed according to this section if all of the following apply:

  (a) The member files a written application with the retirement board within the incentivized retirement application period stating a retirement allowance effective date that is on or after July 1, 2010 but not later than September 1, 2010. A member may withdraw a written application submitted by a member on or before June 11, 2010. A written application submitted by a member and not withdrawn on or before June 11, 2010 is irrevocable.

  (b) On the last day of the month immediately preceding the retirement allowance effective date stated in the application, the member’s combined age and length of credited service is equal to or greater than 80 years or the member is eligible to retire under section 81 with a retirement allowance that is not subject to reduction under section 84(2).

  (c) The member was employed as a public school employee for the 6-month period ending May 1, 2010. A member who has worked in the 6-month period ending May 1, 2010 and is on layoff or on an approved leave of absence status from reporting unit employment is considered to have met the employment requirement of this subdivision.

  (2) Upon his or her retirement as provided in this section, a member who retires with a retirement effective date on or before September 1, 2010 shall receive a retirement allowance equal to the member’s number of years and fraction of a year of credited service multiplied by 1.6% of the member’s final average compensation if the final average compensation is $90,000.00 or less and the member is eligible to retire under section 81 with a retirement allowance that is not subject to reduction under section 84(2). If the member is eligible to retire under section 81 with a retirement allowance that is not subject to reduction under section 84(2) and has a final average compensation that is greater than $90,000.00, the retirement allowance shall be equal to the member’s number of years and fraction of a year of credited service multiplied by 1.6% of his or her final average compensation up to a final average compensation of $90,000.00 and the remaining portion of the retirement allowance shall be equal to the member’s number of years and fraction of a year of credited service multiplied by 1.5% of the portion of final average compensation over $90,000.00. For members eligible under this section because the member’s combined age and length of credited service is equal to or greater than 80 years, upon his or her retirement as provided in this section, a member who retires with a retirement effective date on or before September 1, 2010 shall receive a retirement allowance equal to the member’s number of years and fraction of a year of credited service multiplied by 1.55% of the member’s final average compensation if the final average compensation is $90,000.00 or less. For members eligible to retire under this section because the member’s combined age and length of credited service is equal to or greater than 80 years whose final average compensation is greater than $90,000.00, the retirement allowance shall be calculated so that the member receives a portion of his or her retirement allowance equal to the member’s number of years and fraction of a year of credited service multiplied by 1.55% of his or her final average compensation up to a final average compensation of $90,000.00 and the remaining portion of the retirement allowance shall be calculated as equal to the member’s number of years and fraction of a year of credited service multiplied by 1.5% of the portion of final average compensation over $90,000.00.

  (3) Except as otherwise provided in this subsection, the superintendent for a reporting unit or the chief administrator for a reporting unit that does not have a superintendent may extend the effective date of retirement under subsection (1) of a member employed by that reporting unit to a date not later than September 1, 2011. Each reporting unit having a member who elects to retire under this section may extend the retirement effective date of 1 member under this section. Up to an additional 2,500 extensions shall be allotted to reporting units using a pro-rata methodology determined by the retirement system. The retirement system shall notify reporting units of any additional extension allotments by May 22, 2010. To make an extension under this subsection, the superintendent or chief administrator shall submit to the retirement system notification of members whose retirement dates the superintendent or chief administrator will extend along with the written concurrence of the member on or before June 15, 2010. The superintendent or chief administrator shall not request, and the retirement system shall not implement, the extension of a member that exceeds the number of extensions allotted to his or her reporting unit.

  (4) For purposes of this section, “incentivized retirement application period” means the period beginning on May 19, 2010 and ending on June 11, 2010.

  (5) Any additional costs to the retirement system as a result of the retirement allowance calculations under this section shall be amortized over a 10-year period.