Brihat Parashara Hora Shastra
उत्तमायुः शतादूर्ध्वं ज्ञातव्यं द्विजसत्तम । जनैर्विंशतिवर्षान्त्यमायुर्ज्ञातं न शक्यते ॥ १२॥
Beyond 100 the longevity is called supreme. O excellent of the Brahmins, it is impossible to decide upon longevity till the native is 20 years old.
english translation
uttamAyuH zatAdUrdhvaM jJAtavyaM dvijasattama । janairviMzativarSAntyamAyurjJAtaM na zakyate ॥ 12॥
hk transliteration by Sanscript