Miley Cyrus, 19, is countering critics who think she and fiancé Liam Hemsworth, 22, are too young to get hitched. “Life is too short not to be with the person you want to be with,” she tells September’s Marie Claire. “I don’t really care about the wedding or the piece of paper as much as I do the promise we’ve made to each other. And we want to have a long engagement.” Cyrus says it was a “complete surprise” when Hemsworth popped the question on May 31, but she approves his choice of ring, which reportedly has a hand-cut diamond from the 1880s. “I just love that it’s old and has a story . . . and I’m happy because it doesn’t look like anything else I wear,” she says. With so many celeb breakups in the news, the “Hannah Montana” star adds, “Neither of us is super-jealous. We know each other and would never do anything to hurt each other.”