This was definitely a thing just back in the 2000s. You had guys like melo, tmac, Paul pierce, wade, Dwight ect all decline in this age range or way before. People always mentioned lebron still being so good when he was 33. At first that seemed like an anomaly. Now, you have guys like curry, kd, kawhi, dame, lebron still(lol) jimmy butler, all still being in their prime at 33+. Is it an advancement in technology and medicine? Something else?
Two Main Reasons:
Better Nutrition and Science Medicine Advancements.
Load Management
With the way things are going. Maybe in 2040s-2050s, Superstars will still be good even at age 40-45.