退職 and 辞職: leaving employment and resigning from a position
Compare leaving a company after thirty years with an announced resignation next month, keeping service length distinct from age and timing distinct from completion.
退職: leaving a company and expressing thanks
退職 (たいしょく) means retirement. 「父は三十年勤めた会社を退職し、畑仕事を始めた。」 means “My father retired from the company after thirty years and began farming.” The father left the company after thirty years of employment and began farming. Thirty years is his length of service; the sentence does not give his age, establish a mandatory retirement age, or state his reason for leaving.
「退職の挨拶には、同僚への感謝が丁寧につづられていた。」 means “His retirement message carefully expressed his gratitude to his coworkers.” The retirement message expressed thanks to coworkers with care. Keep this message example separate from the father's story, and do not infer a reason for leaving from the expression of gratitude.
辞職: announcing resignation and its effects
辞職 (じしょく) means resignation. 「部長は会議で、来月末の辞職を正式に伝えた。」 means “At the meeting, the department manager formally announced that he would resign at the end of next month.” The department manager formally announced a resignation at the end of next month. The announcement occurred at the meeting, but the resignation has a future date; it should not be treated as already completed at the meeting.
「責任者の突然の辞職に、職場は一時騒然となった。」 means “The supervisor's sudden resignation briefly unsettled the workplace.” The supervisor's sudden resignation briefly unsettled the workplace. 一時 limits the described reaction to a temporary one. This is a separate event from the manager's announcement for next month.
Distinguish length of service from a future date
Compare 退職 with its focus on leaving employment and 辞職 with its focus on resigning from a position. The English translation “retirement” in these examples does not justify adding a particular age or compulsory retirement cause to every use of 退職.
Read 三十年 as a duration of employment and 来月末 as the announced resignation date. Length of service is not age, and making an announcement does not mean that the stated date has already passed.
What do the thirty years in 三十年勤めた会社を退職した and the end of next month in an announcement of 来月末の辞職 specify?
Show the answer and why
Thirty years specifies the father's service at the company, not his age or reason for leaving. The end of next month specifies the manager's announced resignation date. Keep the completed departure and start of farming separate from the announcement of a future resignation.