How old is Ginny Weasley in the Deathly Hallows?

in the 4th book, she goes to a wizarding school and was allowed in the triwizard tournament, so at that time she was 17 or 18

add 3 years to the deathly hallows and that makes 20-21 which if you were wondering about young marriage is a suitable age to get married in Britain especially when you know that at any moment voldemort could kill you at any moment.