In reality Al Calavicci was 25 years older than his widow Beth.
If counting the first 2 episodes as 1 episode (as a feature length Pilot), the original Quantum Leap (1989)'s 3rd episode (The Right Hand of God - October 24, 1974 (1989)) was also about a boxer.
In addition to being able to leap beyond his own lifetime, Ben is also said to be inhabiting the bodies of the people he leaps into, allowing him to box at an elite level due to the physical conditioning of the host body. In the original Quantum Leap (1989), Sam Beckett physically traveled through time, while the person whose life he was inhabiting would be transported to a chamber at the Quantum Leap project called the "Waiting Room." Sam's body projected an aura so that others would still perceive him to be the person he leapt into, but he was still himself, enabling him to perform feats the leapee would be incapable of (such as a young woman punching out a grown man, or a disabled person walking), including fathering a child with his own DNA. While Ben leaping beyond his own lifetime is given a narrative purpose and addressed by the characters, the alteration to the nature of the leaper/leapee relationship goes unexplained.