Ex 7:7 And Moses was eighty years old and Aaron eighty-three years old when they spoke to Pharaoh.

The advanced ages of Moses and Aaron respectively would only highlight the fact that whatever power or ability they had were not from them inherently but from a divine source --- God. Their infirmity was a stage upon which God's glory would shine brightly through the things that God would accomplish through them. Their seeming disqualification was their very qualification for God to use them. People would say: "Whatever they accomplished could only be from God Himself!"