Born in Nov 2003, Dr. Bennet joined Black Mesa at 18, in 2021. At 80 years old, in Nov 2083, he was used as the test subject in an immortality experiment which was a success. One year later, when he was 81, in Dec 2084, he bore witness to a resonance cascade event, effectively ending his employment. In a panic, he used an experimental time travel device to escape. This experimental machine sent Dr. Bennet 296 years into the past to 1788, just one year before the French Revolution began. Knowing this, Bennet traveled to France to witness it in person.
Dr. Bennet was surprisingly still able to use his communication device to speak to his fellow scientists, despite being 200+ years in the past, hence why he is aware that a few people did survive the Black Mesa incident. Technically, he is still employed at Black Mesa in the present day, 2024, however to avoid a potential time paradox, Dr. Bennet avoids any places where he might meet his younger self, Black Mesa included.
After seeing the French Revolution, Bennet traveled the world, learning many things ranging from musical instruments, languages, martial arts and noteably Pool. He became especially good at gunslinging in the Wild West during the 1800s. He was present all throughout the First and Second World War, and just about every major historical event (within reason) from 1788 to the present day, which for us is May 2025.
As a result, he is now 378 years old.

For more information, message Dr. Bennet.