Ideally. No question in my mind that you should take lessons the very first time you pick up a racket.
The best way to learn is to start with the right grips and the right stances from the first time you try to hit a ball with a racket. My serve has always been a strength because I had lessons early after I started playing and I was shown the continental grip and proper swing pattern.
Also, you're wrong to assume that some players can't hit a ball the first time they pick up a racket. I grew up throwing balls around, hitting things, and running around as a kid. I could hit a ball the first time I picked up a racket, though I wasn't a small child at that point.