Charak Samhita
नर्ते वै षोडशाद्वर्षात् सप्तत्याः परतो न च। आयुष्कामो नरः स्त्रीभिः संयोगं कर्तुमर्हति ॥४०॥
It is not proper for a man, desirous of longevity, to enter in to sexual intercourse with woman when he is under sixteen or over seventy yrs. of age.
english translation
narte vai SoDazAdvarSAt saptatyAH parato na ca। AyuSkAmo naraH strIbhiH saMyogaM kartumarhati ॥40॥
hk transliteration by Sanscript