Both are extremely difficult. But what Mike Tyson accomplished was goddamn ridiculous at age 20. George Foreman had already been the World Champion. He also challenged for a heavyweight title twice and failed during his comeback before winning it on his third attempt. While George's win was a major news story, he had a lot of opportunities. The sanctioning bodies make it even easier for older fighters to get title shots because, if you previously held a world title in a sanctioning body, you can petition them to get a title shot and you don't have to have a ranking first. It's one of the perks of being a former champ of an org. (George Foreman was 45, hadn't won a fight in almost two years, and had lost his last fight a year and a half earlier to Tommy Morrison when the orgs sanctioned his fight with Moorer.) Younger fighters don't have the same advantage. Mike Tyson won the WBC belt a year and eight months after he turned pro. Then unified all the others. Mike didn't fail in two attempts before becoming the youngest champ (like old George did to become the oldest). To break Tyson's record, someone is going to have to come out of the gate really fast and become a world ranked heavyweight in his teens ... and somehow get a title shot. And even if some Olympic Phenom got a gift heavyweight title shot at age 19 or 20 ... I seriously doubt that person would have 27 pro wins before fighting for the world title like 20-year-old Mike Tyson did. (Tyson just tore through the division.) Instead, he'd probably have to be a guy who fought for a world title in his second heavyweight pro fight, or something like that. And, again, I don't see too many 19-year-old Olympic heavyweight gold medalists these days. Also, heavyweights are a lot older in this era. There are 20 fighters older than 40 in the Boxrec top 200 heavyweights. There aren't many heavyweight fighters who are rated and 19 years old. (Boxrec lists 2 who are 19 in the top 200.) So, long story short, seems like it would easier to become the oldest champ as opposed to the youngest. But both are enormous accomplishments, and neither would be remotely easy to pull off.