The fighting Senator and the Legend of Boxing Manny Pacquiao still have the guts to win a TKO, after 9 years he has still power punch. He now a World Champion again, I think he needs one big fight and win again by TKO and then he must retire after that. Ending a career depending his belt would be a better one.
He's not exactly old... I mean, yes, 39 is relatively old in the sport of boxing, but overall he's not even middle-aged yet. He's still got a few years left in him technically, perhaps even 5-6 years if he's careful. Look at Shannon Briggs, Klitschko etc, these are heavyweights that kept going into their 40s, it should be a lot easier for a welterweight.