Former heavyweight champion Mike Tyson has hinted on a possible comeback in a viral workout video posted on his social media account. The 53-year-old Tyson is shown working out at a gym in California and then proclaims "I'm back". He has not had a professional fight since retiring in 2005. 57-year-old former heavyweight champion Evander Holyfield recently floated the idea of fighting his longtime rival Tyson in a charity exhibition.