ENOfficial
Qatadah narrated that `Uthman (رضي الله عنه) was killed when he was ninety years old or eighty-eight years old.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا حَسَنُ بْنُ مُوسَى، حَدَّثَنَا أَبُو هِلَالٍ، حَدَّثَنَا قَتَادَةُ، أَنَّ عُثْمَانَ، قُتِلَ وَهُوَ ابْنُ تِسْعِينَ سَنَةً أَوْ ثَمَانٍ وَثَمَانِينَ.
sunnah.com