Saguaro (pronounced sah-WAH-roe) cacti are very slow growing. These two buddies germinated together about 175 years ago and both are over 30ft tall, and happen to be convieniently located in my driveway. They are home to many local birds who live inside them in holes chipped out by the Gila (pronounced HEE-la) Woodpecker. While not the best photograph in the bunch, I challenge an "honorable mention" category of the *oldest* (living) friends. Those of you who live near bristlecone pines or sequoia can beat me by a couple thousand years.
It's not unlikely that the mesquite tree which is between them, served as the mother plant, sheilding the delicate young saguaro cacti from the sun and cold during the first 15 or 20 years of their lives. So- there are really 3 old friends here.