For awhile, George Foreman’s birthday was said to be some to be January 22, 1948, which would have made the win over Frazier on his 25th birthday. Ring Magazine and numerous press releases listed that as his birthday. Bert Sugar received a birth certificate that showed George’s birthday as January 10, 1949, which is what everyone has gone by since then. https://www.ringtv.com/599813-from-the-archive-george-foreman-is-a-gentle-giant/ https://archive.is/wip/kF7WX https://www.google.com/amp/s/www.latimes.com/archives/la-xpm-1991-03-07-sp-3306-story.html?_amp=true
Tyson was close, his birthday is June 30 Michael Spinks fight: June 27, 1988 Razor Ruddock rematch: June 28, 1991 Evander Holyfield rematch: June 28, 1997
Duran lost on the eve of his 33rd birthday to Hearns so probably had a pretty **** birthday that year.
I’d imagine if you go back to the days when guys fought 20, 30 or more times in a year you’ll find some instances of this (although maybe not significant). In the more modern eras the big fights are mostly on weekends, so you’d have to have a fighter’s birthday on a weekend in that particular year, narrowing the possibilities. But @Italian Stallion I don’t really know fighters’ birthdays so I wouldn’t really know of this. I can’t remember significant fights where that was mentioned during the promotion or broadcast off the top of my head.
I boxrecced this and James Toney, for example, fought twice on his birthday (in 1990 and 1993) but both were 10 rounders and not significant.
Tony Sibson won the British Middleweight Title the day after his 21st birthday. Charlie Nash lost his European Lightweight Title, getting knocked out by Joey Gibilisco on his 30th birthday.