Feelings are often the cause of one's cognition (your internal dialog- what you think as well as what you believe) Your reaction to the event may have triggered issues of self worth, compatibility, feeling disrespected/disregarded etc. The team member's motivation may have not been to cause any sort of harm. Anything could have led to this selection- giving chance to new members, introducing difference/variety, etc. The fact that you're in your 50's actually may be making your reaction stronger than if you were let's say in your 30's. It is possible that this occurrence had caused some doubt within you or you felt discriminated in some way.
As far as how to feel better, it would be helpful to start and monitor your thoughts and to redirect negative and self depreciating thoughts to something negative. As you start to manage your thoughts, your feelings will change. This takes a bit of practice. You can use autosuggestion (a form of self hypnosis) The manual with the techniques is attached here