न तेन वृद्धो भवति येनास्य पलितं शिरः

न तेन वृद्धो भवति येनास्य पलितं शिरः। 

यो वै युवाप्यधीयानस्तं देवाः स्थविरं विदुः। 

इन्द् स्प्रुचे १३८२ हितोपदेशे

na tena vṛddho bhavati yenāsya palitaṁ śiraḥ| 

yo vai yuvāpyadhīyānastaṁ devāḥ sthaviraṁ viduḥ|

 ind spruce 1382 hitopadeśe

A person does not become elderly and would deserve to be addressed senior citizen merely because his hairs have turned snow white with age.

Even gods and men of class would consider a young person who has acquired knowledge and is mature in his outlook is considered old enough and senior enough.