Having been a fan of tennis the past 6 years(im 21), and played for the past 6 years as well.
You may not be able to tell if tennis players are on drugs by size… perhaps they use the drugs to recover faster. Nadal and Serena are both pretty big tennis players. Does that mean drugs or just great genetics or a combination? Too hard to tell IMO. Although Nadal would get my vote prior to Serena.
With a decent workout regime starting at a younger age… I would think it be possible to stand where they do given good genetics as well. Doesn’t hurt to have some chef cook your food all the time either.