Yog And The Flow Of The Four Ashrams
The vedic culture is a very scientific and precise science, science of entire creation and the science of being as a microcosm of the macrocosm which is the physically manifested creation.
I will give a little insight into the vaanprastha stage for a yog-guru. Normally people think that it is renunciation, but there is no such thing as renouncing the world. One goes through it like a ship goes through the ocean, it is on the water and crosses, the water is not in it and so it does not sink. Vaanprastha simply means to begin the process of limiting your interactions with the mundane aspects of life, and with people whose priority is not yog. In vaanprastha, teachings continue and interactions with sadhaks go on. It can be called that the ship is in the middle of the ocean and is moving towards its finality. Those on the ship are limited as only those who trust the ship fully are allowed. How long you have known the ship (guru) is of no consequence, your desire and other prerequisites are important.
Having collected the force within for the onwards journey in the years of brahmcharya and having gone through the experiences of a worldly life as a grihasta, a being takes a step back from the physical world as he enters vaanprastha, because to reach the final destination, all this has to be left behind. For a rocket to break the pull of gravity, it has to leave its excess weight. Leaving does not imply running away, the thought of the physical has to go.
Let me explain this with the help of the example of a rishi who left his family and house to do dhyan in Himalayas. The rishi followed a niyam of offering milk to the shivling every day. As he went to the Himalayas, commoners from nearby villages would bring him milk and he would carry on with his practice. Once no one came to give the milk. In the absence of milk, the rishi offered water to the shivling. However, it soon became a common occurring, the villagers would often forget to bring him milk.
The rishi then decided to keep a cow so that he does not have to depend on the villagers. When he went to village to get the cow, the villagers advised him to also take a lady with him to take care of the cow as he would be in dhyan for long hours. The rishi agreed. Five years passed. The villagers then asked the rishi to marry the lady since no one else would take her. The rishi agreed. He married her and they had a family. So, whatever he had left, was created back again for him because of his one thought. That is why it is said, yogah chitt vritti nirodh. One needs to silence the modifications of the mind to access what lies beyond the five senses. Vaanprastha is preparatory stage which further leads to sanyas.