I would first congratulate your teacher on wanting to protect her students. However, I do have several concerns with her reasoning:
1) She is grouping all her students into one large category--a fragile group, and treating the healthiest older student the same as a frail student. Certainly there are students for whom longer holds are not a good idea, but for most students there is no fear. By treating everyone the same, she is protecting (maybe) 1 or 2 students but at the expense of helping all the others. (Please read my article on Antifragility
2) The body is constantly repairing micro-tears. This is normal even for elderly. Resistance training (weights etc) create microscopic tears in the muscles, and the body initiates a healing cascade of events: secreting growth hormones and other cytokines to repair the damage. In the processes these messenger molecules leak out into the general blood system and stimulate healing throughout the body. Thus we find that the body become stronger after stress than before the stress (to a limit of course! We can always over stress the body.) (Check out this study
for more details.)
3) I do not believe any acupuncturist follows her philosophy and reduces the time the needles are in to 2 minutes simply because the patient is over 55
4) The work of researchers (like Helen Langevin
) have shown that long held fascial stresses are very beneficial.
5) A limit of 2 minutes means that this practice is not really affecting the yin tissues...it takes at least 2~4 to start to stress these targeted tissues.
I could go on and on, but my final point would be -- it is really up to the student to make this determination. At best the teacher helps the student learn to notice when the time is too much or not enough. The training begins by asking "what are you feeling?" If there is pain, then regardless of the age, the student should come out. But if there is no pain while in the pose, when coming out of the pose or even the next day, then the practice is most likely very safe.
I hope this helps.