We can approach this question from two directions, chronologically and psychologically. Chronologically, the starting point is the age at which people traditionally begin Yoga practice.
“A person is fit to practice when they can eat by themselves.”
– Śrī Krishnamacharya
According to the Yoga teachings of T Krishnamacharya there are three chronological stages of life, or Tri Krama.
This is the stage to develop the body and practice lots and lots of Āsana, and obviously, with very young people their interest and attention will be more engaged by using a wide range of challenging Āsana and utilising Āsana sequences involving jumping and other challenging techniques.
This is the life stage context within which, perhaps, Mr Iyengar and Pattabhi Jois would have studied. According to Krishnamacharya this stage ended at about 24 and then you moved into relationship, work and family life.
When you are in the work, relationship and family lifeplace, who has time to practice Āsana three hours a day? Priorities change. There is a teaching from T Krishnamacharya around this called the Yoga Rahasya, which says that when you are a family person you have to look after your family, your work, your relatives, the priest, the beggar… what time is there to look after yourself?
2. During this time there is also a developmental shift. You’ve got the Āsana under your belt, so to speak, and now the priority is to maintain your energy or Prāṇa Śakti. Yoga practice is now prioritised for sustaining energetic, mental and emotional stability. This stage is known as Sthiti Krama where the need is more psychological than physiological.
Your early Āsana training supports your physical vitality and health, however it is now time to sustain your psychological vitality, so Prāṇāyāma is now the primary focus with Āsana a secondary priority.
3. The third stage, Antya Krama or final life phase is when priorities shift yet again. If you have children they are grown and flown, you don’t have the same ambitions in your workplace, your relationship with immortality shifts towards a relationship with mortality. It is no longer the outside world, it is the inside world that is of more interest. Our life perspective downsizes and internalises.
The question is how to support that change in body, breath, mind and emotions? In the first stage the priority was physiological, in the second stage it was psychological, and in this third stage the priority is now more spiritual.
So in the third stage, Āsana and Prāṇāyāma still have their place, but the focus is much more around the idea of Dhyānam or meditation, inquiring into the question of what is the meaning of death, cultivating insight into the nature of nature in order to realise what is not nature and coming to terms with it before dying and being reabsorbed into the ultimate matrix.
“Initially our Yoga Sādhana is about our relationship with living.
Ultimately our Yoga Sādhana is about our relationship with dying.”