Gregg Allman, 64, Engaged To 24-Yr-Old Girlfriend. 25 May 2012 3:22 PM, PDT | Entertainment Tonight | See recent Entertainment Tonight news Â». Perhaps the seventh time's the charm for Allman Brother's founding member, Gregg Allman. The rocker revealed on Piers Morgan Tonight that he plans to give the institution one more shot-- this time with fiancÃ©e Shannon Williams, who is 40 years his junior.