No member of the police department who shall become unable mentally or physically to perform the person‘s duties, nor the person’s dependents, shall be entitled to receive benefits under this chapter because of such disability unless such member shall have been on active duty with the department for a period of at least ten years prior to such disability unless such mental or physical impairment was received in the line of duty and permanently disabled such member. Provided, however, that any member of the department who shall have served twenty-two years, retired, and subsequently suffered a permanent disability prior to attaining age sixty, may, in the discretion of the pension board and providing that the same is actuarially sound, be eligible for disability retirement. The question of disability shall be determined by the board of trustees upon the concurring report of at least two out of three physicians designated by the board of trustees to make a complete physical examination of the member.