In plain words
Your stages keep moving from moment to moment. Childhood, youth, adolescence, old age: all four stages move on within moments. But though the stages are different, the person stays one and the same. One and the same person goes through these four stages.
All these we may compare to tṛṣṇā itself. You want education. That is a tṛṣṇā. You want a job: that too is a tṛṣṇā. You want to marry: that too is a tṛṣṇā. You want children: that too is tṛṣṇā. Mother, father, job, fame and honour: all these belong to tṛṣṇā. This tṛṣṇā is simply like strong fetters. When time, karma, cause and duty come together, even iron fetters may rust with the change of time and grow weak. But as time passes, tṛṣṇā only grows tighter; weakness never comes to it. So first of all we must try to curb our desires.
In daily life there are certain rules for following a true path. In everything one Satya flows as an undercurrent, at one with it and held within it. You must try to recognise the truth in your studies too. 2+2=4. Ten thousand years ago, ten thousand years from now, in the conditions of today, in whatever country, at whatever time, this truth does not change. However much time passes, whatever country you go to, in whatever circumstances, under whatever government, 2+2=4: this is the truth of mathematics. And the truth of physics is like this: when we take a needle and hold it near a candle, the needle grows larger. This is a truth of physical science. The truth of chemistry is like this: when lime and turmeric are mixed together, a red colour comes out. This is true for all time. It is not something that changes. Then there is the truth of botany. When we take a glass and set a plant in it with its roots upward and its stem downward, it grows well. The truths of mathematics, chemistry, physics and botany never change. Science can carry its research to higher and higher levels, but it cannot change what is.
In the same way, in man's nature too there is something that does not change. But in whatever circumstances, whatever country he goes to, whatever work he does, whatever situation he is in, he wants Ānanda. That is the great desire. The reason is that Ānanda is his very form. It is his very nature; so there is no man in the world who does not long for his own form and his own nature. So man longs for the ending of sorrow and the gaining of Ānanda.