Permanent firemen as of March 27, 1947, the date of the passage of this section, who were heretofore unable to accept the provisions of this chapter at the time of becoming permanent firemen, because they were then over 35 years of age, which limitation was in effect prior to March 27, 1947, may accept this chapter and make application to the retirement board as provided in N.H. Rev. Stat. § 102:4, within 30 days after March 27, 1947 and not thereafter. The assessments upon the salaries of such over-age permanent firemen shall be fixed by the retirement board as provided in N.H. Rev. Stat. § 102:9. Any person under 45 years of age who becomes a permanent fireman after July 1, 1965 shall be deemed to have accepted the provisions of this chapter and to have consented to assessments upon his annual salary as determined by the retirement board, as a condition of employment.