The oldest British Queen is Queen Elizabeth II (UK, b. 21 April 1926), who took the record from her great, great grandmother, Queen Victoria (1819-1901), on 21 December 2007 aged 81 years 244 days.

Offically, Queen Elizabeth surpassed Queen Victoria at 5 pm GMT on 20 December 2007 (taking into account Queen Victoria’s hour of birth and death). I went with the next day, otherwise would be an equal holder.

If still on the throne, Queen Elizabeth will surpass Queen Victoria’s record for the longest reigning British monarch on 9 September 2015.