In verse 46, thamānīna ḥawlan gives the fatigue of old age a concrete duration: eighty years. Ḥawl means a year. The line is a poetic generalization about long life, not a biological prediction about every person who reaches that age.
Lā abā laka functions as forceful traditional address. The first-person “saʾimtu” grounds the observation in the poet’s experience, while “man yaʿish” broadens it into a proverbial statement.