Why didn't Laman and Lemuel stay in Jerusalem?

[Damasta]

I know a lot of people are influenced by the <i>Living Scriptures</i> depictions of Nephi, Laman, Lemuel, &c., but I always figured that Nephi was only like 13 or 14 when Lehi had his vision of the destruction of Jerusalem. And that Laman and Lemuel were both 18 or under (in fact, I have a tenuous theory that they might've been twins, but I digress). That being the case, they didn't say in Jerusalem because were too young to have the moxy to run away. That and I've heard that sons didn't usually marry and leave their parents tent until they were around 30 (I don't have a reliable source for that information, though, so disregard as you please).