There are four phases in the life of a Hindu. Initially a Hindu is in what's called the Brahmacharya (student) phase, until they are 24 years old. During this time they focus on education and includes the practice of celibacy. The next stage of life is Grihastha (household), and lasts another 24 years. It's when a Hindu gets married, maintains a family and raises children.
In the third phase of a life, Vanaprastha (retired), a Hindu hands over their household duties and gradually withdraws from the world. This phase, like the two before it, lasts for another 24 years. Finally, the last phase Sannyasa (renounced life) is where a Hindu detaches from material life, without any meaningful property and not even a home necessarily. This, is the phase of life in which you will find Sadhus.
Now of course, not everyone follows the path of religion and becomes a Sadhu. Technically you only need to have passed the first phase in life to enter the final stage, although I'm not sure how common it is. Then again, there are always people that find religion later on in life, so I have to imagine it does happen.