The phrase "of many/five/ten etc. years' standing" is commonly used to describe something or someone that has been in existence, operation, or occupation for a long time. However, if you want to avoid repetition or add some variety to your writing, you can use synonyms for this phrase. For example, you could say "long-established," "long-standing," "well-established," "veteran," "seasoned," "experienced," "mature," "time-honored," or "deep-rooted." These alternatives convey a similar meaning and can help you avoid redundancy and make your writing more interesting. So, next time you come across the phrase "of many/five/ten etc. years' standing," consider using a synonym instead.