Pharmies or working out/sleeping/eating right. Staying up late to gamble he does not.
In my mind, it's probably all of the above. Lebron reportedly spends $1 million per year working on his body. My guess is that a percentage of that might include a few designer "supplements". Of course, I feel the same way about Tom Brady, which I know is a very taboo topic in Boston. I just don't think that clean living adds 10 years to somebody's prime, even among the best of the best.
I personally wouldn't be opposed to leagues allowing monitored PED use, particularly for recovery purposes. They're modern medicine and can be safe and effective if used properly. But, I do suspect that a lot of athletes' longevity is a result of dabbling with drugs that are legally prohibited.
except we don't really see players playing longer. In fact they play less games, less minutes, and generally the same amount of years. Every generation seems to have a player or a few that are quite simply genetic freaks of nature. You had Wilt (didn't get the years, but was the greatest physical specimen the league has ever seen), you had Kareem, you had Malone, you had Duncan/Kobe/KG, and you have Lebron. Those guys just took care of themselves and were professional off the floor as well as on it (when it comes to fitness). That helps a great deal, but even then you just have to have the right genetics and a certain amount of luck to avoid the devastating injury.
I have no idea if Lebron is using, but I suspect most players are and have been since the dawn of performance enhancing drugs, but only a handful end up with the longevity and skill necessary to play at a high level for 20 years.