On and after January 1, 2013, a person who has retired for disability and has not attained the mandatory age for retirement for persons in the employment in which he or she will be employed, and whom the board finds is not disabled for that employment, may be so employed by any employer without reinstatement from retirement if the position is not the position from which this person retired or a position in the same member classification. The person’s disability retirement pension shall be reduced during this employment to an amount that, when added to the compensation received, equals the maximum compensation earnable by a person holding the position that he or she held at the time of retirement. This employment shall terminate upon the person’s attainment of the mandatory retirement age

for persons in that employment. A person employed under this section shall not be concurrently employed under this article.