She has just less than two years to go to overtake Louis XIV of France into first place which would occur on 27 May 2024 at which point she will have been reigning for 72 years and 111 days, 1 day longer than King Louis and will be 98 years and 36 days old.
This would actually happen on 26 May 2024 when Her Majesty’s reign would be 26,408 days to Louis XIV’s 26,407.