Brennan's success with "The Real McCoys" led to him making a few recordings, the most popular being "Old Rivers", about an old farmer and his mule, which was released as a single in 1962 by Liberty Records with "The Epic Ride of John H. Glenn" on the flip side. "Old Rivers" peaked at number five in the U.S. "Billboard" chart, making the 67 year-old Brennan the oldest living person to have a Top 40 hit at the time, in fact, the oldest living person to have a top 5 hit. At age 68, Brennan reached the Top 40 again, this time with "Mama Sang a Song" on 17 November 1962.