Thinking of going back to college to pursue a second career as a college instructor? Expect your professors to be older than you are — maybe even well past retirement age. And take note that a bottleneck is forming in the professorial ranks as more retirement-age profs decide to keep teaching.

That's the nugget from a recent Fidelity Investments survey of nearly 200 full- and part-time college professors who were eligible for retirement benefits. Three-quarters of professors in the 49- to 67-year-old age range said they will either delay their retirement beyond when they could take it, or have decided not to retire at all.

The implications for the university-level teaching profession are significant. As more aging profs hang on to their book-lined offices, those coming up are going to have to wait longer to get started and be more patient as they seek tenure, that most golden of university employment rings.