Dragon Ball Super was the canonical introduction of the fan-favorite Legendary Super Saiyan Broly, years after his original appearances in non-canonical movies and video games during the Dragon Ball Z era. And while the latest iteration of Broly is easily the most powerful the Super Saiyan has ever been, he also hides a rather startling secret: Despite being more formidable than ever, this Legendary Super Saiyan is actually well into his 40s, despite his relatively youthful depiction in the movie Dragon Ball Super: Broly.
The movie reveals that Broly was born within days of Prince Vegeta — approximately five years before Goku and the destruction of the Saiyan homeworld. This puts Broly at the same age as Vegeta, growing up with his father Paragus on a harsh, remote planet after Planet Vegeta's fall at the hands of Frieza. With Vegeta about five years old when his home planet was destroyed, this makes Broly around 28 years old at the start of DBZ. With Super taking place within the ten-year time jump between the final battle against Kid Buu and an epilogue centered on the 28th World Martial Arts Tournament, Vegeta and Broly are around 39 at the start of Super and well into their 40s by the time of the Broly animated movie.
The original, non-canon Broly's origin was tied directly to Goku rather than Vegeta, with the two lower class Saiyan infants born on the exact same day. Goku's innate fighting spirit led to incessant crying, upsetting Broly and deeply traumatizing him, which carried over to the pair's reunion as rival adults. In contrast to being introduced shortly after the events of the main Dragon Ball Super anime series, the non-canonical Broly was introduced in the ten days leading up to the Cell Games. This makes the original Broly around 27 years old when he meets the Z Fighters and 34 years old at the time of his death in the animated movie Dragon Ball Z: Broly - Second Coming.
While both Vegeta and Broly are middle-aged in the Dragon Ball Super movie, they both clearly haven't missed a step. This is because Saiyans age at a much slower rate than humans as an inherited genetic trait befitting their status as a warrior race. By the end of DBZ, years after the events of Super as Vegeta approached 50, the Saiyan Prince was physically unchanged since his fight against Kid Buu a decade before at the age of 39. This genetic trait ensures that Saiyans stay in their physical prime longer to be able to fight at their best for decades, not showing visible age until they're closer to their 70s.
The canonical Broly appears younger than Goku and Vegeta, coming across as a teenager or young adult, rather than someone well into their physical prime, much less as someone in their 40s. Thanks to his pure-blooded Saiyan genetics, Broly won't be showing his true age anytime soon as he continues to grow stronger with every successive fight. The movie certainly leaves the door open for Broly's return, potentially in a time period after the end of DBZ as the series charts a new future. That said, given how youthful Goku and Vegeta look at the end of the original series thanks to that Saiyan fountain of youth, Broly will likely be just as fresh-faced as ever when he inevitably resurfaces.