The young guns often have great questions, that help you either reinforce the knowledge you have, and occasionally, can even challenge your own knowledge, opinion, and judgement so you change your outlook.
To teach something is the final step in learning/understanding/mastery of a topic.
I've just hired my first guy a few months ago, its painful at times but it gives me a great perspective on how far i've come since graduating.
Also, someone did it for me, now i'm giving back.[pre][/pre]