As Andrew says, it means he managed to get his first film role. To 'land' something is a fishing metaphor. If you land a big fish, you manage to catch it. It is used when someone is lucky or skillful enough to secure a great prize of some kind.

It means he managed to get his first film role at 20.

http://www.oxforddictionaries.com/us/definition/learner/land Verb, definition 7