TTR has a good op-ed in Economic Times.
Retirement age is just one of the points in the op-ed; and it's not even the most important point -- restricting the tenure at the helm to just one term is. The reasons cited by TTR are quite compelling:
there is a weighty reason for not having a higher retirement age and a second or third term for directors: in the IIT system (and also in the IIM system), there is very little accountability of directors. Lack of accountability of the director is the principal governance issue in our elite institutions today, not any supposed lack of autonomy.
Over the years, the boards of these institutions have failed to put in place adequate norms for accountability of the director. In the past couple of years, the ministry of HRD has tried very hard to bring this issue to the fore, but we are yet to see any results.
The contrast with top institutions in the US ... [where] ... the deans are ... subject to a high degree of accountability. A failure to improve the faculty profile, the departure of faculty of stature, a fall in programme rankings, a decline in the quality of research —these and other failures could easily cost the dean his job. In India, it is possible for the director of an elite institution to sleep through his tenure without evoking any response from the system.