Detailed Instructions: In this task you will be given an answer to a question. You need to generate a question. The answer given should be a correct answer for the generated question.
Q: The absence of a mandatory retirement age contributes to 'graying' of this occupation. The median age of American full professors (in 2006) was around 55 years. Very few people attain this position before the age of 40. The annual salary of full professors averages at $99,000, although less so at non-doctoral institutions, and more so at private doctoral institutions (not including side income from grants and consulting, which can be substantial in some fields); in addition, institutions in major cities or high cost of living areas will pay higher salaries. Full professors earn on average about 70% more than assistant professors in the same institution.
A:
what is the retirement age for professors in usa