Section 7. The state facilities under the control of the department shall be such state hospitals, mental health centers and other mental health facilities as the commissioner from time to time shall designate in the regulations of the department, including any facilities or portions thereof which the department may, subject to appropriation, construct or develop for use as homes or facilities for aging persons who are not mentally ill. Admissions of patients to said facilities or homes for aging persons shall be voluntary and not by commitment and said facilities or homes, although under the supervision and control of said department, shall be deemed to be public medical institutions within the meaning of section two of chapter one hundred and eighteen E.