A fair point, but I dare say Socrates didn't use an English language dictionary. Perhaps there's a more accurate way to translate the quote from ancient Greek.

No that's not what it means at all. An amateur is not a beginner. The word is being used here to convey a level of commitment and discipline, not a level of ability.

The intent here is that you approach your health and physical fitness with dedication, discipline, commitment, and sacrifice. Amateurs don't take that approach. They aren't serious about developing themselves. They make excuses or find reasons not to train.

Regardless, you don't have to be Hercules to go to a gym. You just have to want to be healthier and fitter. Strive to be best YOU can be. Any improvement at all is worth it.