Allah, the Exalted, says:
"Did We not give you lives long enough, so that whosoever would receive admonition, - could receive it? And the warner came to you." (35:37)
Ibn `Abbas and others said that "long enough" in the Verse means sixty years. The Hadith which follows supports this. Others said it means eighteen years; Al-Hasan Al-Basri, Al-Kalbi and Masruq said it means forty years, it has also been reported by Ibn Abbas and others that whenever the people of Al-Madinah turned forty years of age, they would devote themselves completely to worship. "Long enough" in the Verse has also been interpreted to mean the age of puberty. Ibn `Abbas and the majority of Muslim scholars said that the "warner" in the Verse refers to the Prophet (PBUH). `Ikrimah bin `Umaiyyah and others interpreted this word as the grayness or whiteness of hair. Allah knows better.