I need this information for a story that I'm writing, so it doesn't have to be perfectly scientific. Just a round-about answer would be great! Thanks!!

It's a hard question to answer, partly because there are about 80 different kinds of magnolias in the u.s. The Southern Magnolia - the one probably most people think of when they hear "magnolia" can keep growing for 80-120 years. So- a long time.