I don't want to rekindle/continue an old friendship
Why don't you want to rekindle that friendship?
We've disliked each other for years and have grown distant.
It's understandable to want to end a friendship that no longer works, but you should do it in a manner where you both get closure. That way you can both accept it and move on.
Our friendship lasted over 50 years.
Well, all good things come to an end at some point.  It's up to you to decide whether that point is now.  I just suggest you communicate your decision to your friend regardless of what i ends up being.