The phrase "grand daddies" can be used to describe old or experienced individuals, but there are many different synonyms that can be used instead. Some possible alternatives include "elders," "veterans," "patriarchs," "sages," "wise men," "gurus," "masters," "pros," "experts," and "legends." Depending on the context in which you are using the term, there may be a specific word that is more appropriate or that conveys a particular connotation. In any case, by using a variety of synonyms, you can add variety and nuance to your writing and avoid repeating the same phrase over and over again.