Jami` at-Tirmidhi Book 49, Hadith 19

"The Messenger of Allah (ﷺ) was not very tall nor was he short, nor was he pale white, nor was he brown, nor was the wave of his hair completely curly nor straight. Allah sent him at the beginning of his forties and he stayed in Makkah for ten years, and in Al-Madinah for ten years. And Allah took him at the beginning of his sixties, and there were not more than twenty white hairs on his head or in his beard."