I was reading that it's a good idea to wait, because your gains in each category are random and you could possibly be using feed in a category that raises faster than others. Mine, for example is a 19 star (stamina is lacking one). But here are my stats at rank 19:
Speed 115/500
Acc 115/500
End 145/500
Stam 147 460
Cun 150/500

So as you can see, they don't level up the same. I will probably end up plugging in more feed into my Speed since it's lower. I just don't want you to waste food on a stat that could reach max with a few less feedings.

Note: I have used no feedings yet