By retirement, my father will have worked about 30 years.
Literal
Father [topic-は], mandatory-retirement [by-までに] about 30-years work thing [result-に] becomes.
定年 (ていねん) means 'mandatory retirement age' — a key concept in Japanese work culture. ~までに sets the deadline. ~ことになる indicates a resulting situation that develops naturally: 'it will turn out that he will have worked 30 years.'