Answer
You have spoken the truth. In reality, such individuals do not need to go to the forest and take formal sannyasa; rather, they need to become sannyasis while living in this very world — sannyasis of the mind.
Lord Krishna remained on earth in His body for 125 years, yet He never took sannyasa. Shri Rama, too, never took sannyasa.
In the Bhagavad Gita, the Lord says that a person who has become mentally detached from this world and has united himself with God while living in this very world — such a Karma Yogi should also be regarded as a true sannyasi.
You will observe that at different ages, a person's natural inclinations also change. In childhood, a child cries intensely for toys and is deeply attached to them. In adolescence, one begins to be attracted toward the opposite sex. In youth, the natural tendency is toward marriage and building a family. Then, as old age approached, the attraction to sensory pleasures would diminish, and the person would become more inclined toward God and spirituality.
However, in recent decades, people have become so attached to sensory indulgences and so attracted to comforts and conveniences that even in old age they do not wish to turn toward God. Through television and mobile phones, their engagement with the world has only deepened. But gradually, times are changing again, and a Hindu renaissance is underway. Even people in the West have grown weary of their own culture, and within them too, an attraction toward Indian cultural values is growing.
In truth, the depth that exists within Sanatan Dharma is found nowhere else. Therefore, all those who have reached the age of fifty should gradually and seriously enter the realm of spirituality. If truth be told, spirituality has no age. Wise people remain connected to spirituality from childhood and through youth — and indeed they should. After fifty, one should most certainly engage with it in a dedicated manner.
When a person forms a genuine connection with God, he does not experience loneliness or depression.