A man is as old as he feels

एकोऽहमसहायोऽहम्
कृशोऽहमपरिच्छदः ।
स्वप्नेऽप्येवंविधा चिन्ता
मृगेन्द्रस्य न जायते ॥

"I am alone and helpless. I am old and destite." Such thoughts do not worry a lion even in its dreams.

A man is as old as he feels himself to be.