Unless he suffered a heart attack or some such incident and lost control of his tractor,..."age" really doesn't have much to do with it. Could have happened to anyone foolish enough to drive close enough to the edge of a 4 ft creek bank to have a wheel slide off or the edge crumble under the tire etc.
The one big lesson here, (in MHO) is "be aware" of your underpinnings,... even a "dry" creek bank can quickly crumble beneath your tire. And a "wet" creek bank can slide you down like a magnet to the creek or lake etc!
Other than that,...to me,..its just a very sad occurrence,..I hope it was quick!!
Be Aware of your underpinnings !!!
. . tug