From Sahih Bukhari (Hadith 2366):
Narrated Sahl bin Sa`d:Once a tumbler (full of milk or water) was brought to Allah's Messenger (ﷺ) who drank from it, while on his right side there was sitting a boy who was the youngest of those who were present, and on his left side there were old men. The Prophet (ﷺ) asked, "O boy ! Do you allow me to give (the drink) to the elder people (first)?" The boy said, "I will not prefer anybody to have my share from you, O Allah's Apostle!" So, he gave it to the boy
Reference: Bukhari 2366