For me to tell you to not worry would be highly hypocritical of me. As parents of kids these days, we worry.
My baby graduated college in May, came home for a few weeks, and before I knew it she was loading up her belongings in the back of her car to head to Washington state to start the next chapter of her life, 3000+ miles away. She's coming home for Christmas and that's the greatest gift I could possibly receive! 🙂
It's just part of the process. We do our best to raise our kids right, teach them to make good decisions, surround themselves with good people they keep company with.
I'm sure he'll be fine. My sister-in-law and her husband live in Japan, have been there for 30 years. They love the culture there. It'll be a great learning experience for him!