Imam Sadiq (a.s) said: “It is not proper to kiss a girl once she reaches the age of six.”
وعنه (عليه السلام) قال
إذا بلغت الجارية ست سنين فلا ينبغي لك أن تقبلها.
Similar narrations
Al-Kāfi #2030“Abu ‘Abd Allah (a.s.), has said, ‘When a free girl becomes six years old then it is not proper for you to kiss her.’”
Man Lā Yaḥḍuruh al-Faqīh #1295"When a girl reaches six years of age, a boy should not kiss her, and a boy should not kiss a woman once he passes seven years of age."