Kamasutra 1.2.5

1.2.5

anityatvād āyuṣo yathopapādaṃ vā seveta//

Man, the period of whose life is one hundred years, should practice Dharma, Artha, and Kama at different times and in such a manner that they may harmonize together and not clash in any way. He should acquire learning in his childhood, in his youth and middle age he should attend to Artha and Kama, and in his old age he should perform Dharma, and thus seek to gain Moksha, i.e., release from further transmigration. Or, on account of the uncertainty of life, he may practice them at times when they are enjoined to be practiced. But one thing is to be noted, he should lead the life of a religious student until he finishes his education.