It is narrated from Sayyiduna Malik bin al-Huwayrith (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The eldest of the people in age should lead them in prayer." And when Sayyiduna Malik bin al-Huwayrith (may Allah be pleased with him) raised his head from the second prostration, he would sit, then rise.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16685