The oldest mtDNA in Europe which is human (i.e. Homo Sapiens and not Neanderthal or other archaic individual) is U5 and U8a (see below). The age of U5 is estimated at 50,000 but could be as old as 60,500 years. Approximately 11% of total Europeans and 10% of European-Americans are in haplogroup U5.
The presence of haplogroup U5 in Europe pre-dates the expansion of agriculture in Europe. Bryan Sykes' popular book The Seven Daughters of Eve says it shows up 45,000-50,000 years ago in Delphi, Greece and named the originator of haplogroup U5 Ursula. It shows that U5 is the first out of Africa into Europe, and that it shows up as the first Europeans in two places, Delphi and Spain around 50,000 years ago.
By another source haplogroup U5, age is estimated at about 52,000 kya, being the oldest subclade of haplogroup U.[8]
Haplogroup U5 and its subclades U5a and U5b form the highest population concentrations in the far north, in Sami, Finns, and Estonians, but it is spread widely at lower levels throughout Europe. This distribution, and the age of the haplogroup, indicate individuals from this haplogroup were part of the initial expansion tracking the retreat of ice sheets from Europe ~10kya.
Haplogroup U5 is found also in small frequencies and at much lower diversity in the Near East and parts of Africa, suggesting back-migration of people from northern Europe to the south.[1]
Mitochondrial haplogroup U5a has also been associated with HIV infected individuals displaying accelerated progression to AIDS and death.[9]
U5 and U6 are "sister mtDNA groups" with a common ancestor (probably in West Asia).