Charak Samhita
आद्वादशात् स्यात् प्रसृताभिवृद्धिरष्टादशाद् द्वादशतः परं स्युः। आसप्ततेस्तद्विहितं प्रमाणमतः परं षोडशवद्विधेयम्॥३२॥
then increase oneprasrita till 18th year, reaching the maximum dose i.e., twelveprasrita. The dose after 70 years is equal to the dose of 16th year.
english translation
AdvAdazAt syAt prasRtAbhivRddhiraSTAdazAd dvAdazataH paraM syuH। AsaptatestadvihitaM pramANamataH paraM SoDazavadvidheyam॥32॥
hk transliteration by Sanscript