Your first step is earning your PADI Open Water Diver certification becoming what is commonly known as a “certified diver.”
Even if you’ve previously taken part in introductory scuba experiences (commonly known as “resort courses”), you are most likely aware that the best opportunities in diving await those who are fully certified.
Fortunately, most people young and old qualify to become certified. Not a famous swimmer or athlete? That's OK too. Will medical conditions disqualify you from diving? The answer to all these questions is generally No.