Miley Cyrus may not, or may still, be getting married to Liam Hemsworth. Cyrus is 20, and got engaged at 19, while Hemsworth is just barely older, at 23. If that seems to you an unspeakably young age for marriage (not mention a patently bad idea), it’s probably because you don’t reside in one of two worlds: the celebrity sphere or the 1950s. After all, a new study on marriage trends shows that the marrying age in the U.S. keeps going up. But pop stars, as in so many other aspects of life, play by different rules.