Miey Cyrus is 19 and engaged to the HOT Liam Hensworth from The Hunger Games. Sadly, to bite a line from "The Hunger Games" - "the odds are not in their favor". [Love that movie BTW.]
Let's take a look at some other young Hollywood couples - did they make it?
Jessica Simpson (22) and Nick Lachey. They divorced when she was 25.

Kate Hudson (21) and Chris Robinson. They divorced when she was 28.

LeAnne Rimes (19), Drew Barrymore (19), Macaulay Culkin (17) - ALL DIVORCED within a few years.

But I will give a hat-tip to the classy Bo Derek, she married John Derek at 18, he died in '98 with her by his side.