I hired a person who I've known for 11 years, and know full well he's a "one-upper".?

This man is horribly insecure and craves approval. Since you hired him knowing of his affinity for one-upping, just do your best to tolerate it, especially since you have confidence in him doing the job you want done. His age is irrelevant. You are in charge. But since he needs constant reurance, you might go out of your way once in a while (before he starts his crap) and give him a pat on the back for a job well done. Then he might not feel the need to sing his own praises. Then again, you might occasionally give him a jab with "Now lets hear from (name)." When it becomes too taxing, then pull him aside and tell him to tone down the bragging because everyone contributes, not just him. The very worst thing you can do is to put him down or criticize him. That will only poke at his insecurity and make him even more competitive. Good luck!