5.7% is better than most.
As to that website, Ellis Toussier isn't even a diabetic. He's an idiot, using insulin to get his own HbA1c down into the 4s.
There's precious little work been done on what constitutes a "normal2 HbA1c in non-diabetics, but 1 set of figures I found give an average of 5.1%.
It may well be that "ideal" is in the 4s, but it's difficult to achieve and needs care and knowledge to do it safely,
I wouldn't say that you shouldn't keep it as an ambition, but you are still new to all this and most people would be delighted to get your numbers so quickly
Hana