Гламурное Кисо
We know this because in August 1995, Tonks tells Harry she's only one year out of Auror training (OP3). Since this training takes three years (OP29), she must have finished school in 1991 - putting her date of birth in 1972 or 1973.

Выходит что таки поступила в 1991. Год нигде не шаталась:
Tonks says in 1995 Harry Potter and the Order of the Phoenix, Chapter 3 (The Advance Guard) "I only qualified a year ago" and Auror training takes three years after graduating Harry Potter and the Order of the Phoenix, Chapter 29 (Careers Advice) - "...Auror training takes a further three years...") placing Tonks' graduation in 1991 (if she immediately started Auror training), and her birth in late 1972 or 1973