Vaisesika Sūtra 6.2.03

चातुराश्रम्यमुपधा अनुपधाश्च ॥३॥

cāturāśramyam-upadhā anupadhāś-ca ॥3॥

[चातुराश्रम्यम् (cāturāśramyam) - the fourfold system of life stages; उपधा (upadhā) - obstacle; अनुपधा (anupadhā) - non obstacle; च (ca) - and;]

The fourfold life stage system consists of obstacles and non obstacles.