. >> solman: at george mason university, 71-year-old writing professor don gallehr is still teaching too. >> if the kids are happy and learning and i'm happy and learning, i'm here. >> solman: and how long does 69- year-old boston university particle physicist larry sulak plan to keep blowing up protons? >> i have no idea. shelly is a good model. >> solman: that would be his 80- year-old colleague, nobel- winning physicist sheldon glashow. and when do you intend to retire? >> that i don't know. >> solman: america's work force is graying, and academia along with it. professors over 65 have more than doubled since 2000. some 40% of all workers say they'll work past 65. in academia, however, a full 75% plan to work past a normal retirement age. historian claire potter is at the new school in new york. >> most of us believe that we should be able to work on our own terms for as long as we want. >> solman: potter blames lifetime tenure, meant to protect professors from political firings, and the legal end to mandatory retirement in 1994. but potter insists she'll be different. >> i'm goin