I know just how you feel Karen. My daughter went out to Australia on her own a few years ago now. Couldn't quite believe it was happening til it did but, after a few hiccups in the first few weeks, she settled down and found herself a good job at the ANZ Stadium in Sydney and had a great time. She's back home again now, well living in London, but still talks about going back sometime.
I'm sure your son will be fine and have a great time himself.
How long is he planning on going for?