I'm going to go out on a limb here and claim that humans have been able to count since
before you'd consider them human.
Lots of animals are able to count and it's ridiculous to assume that any individual with even a rudimentary language wouldn't be able to.
With which I mean to say that you don't need a formal understanding of 'mathematics' to count.
Further there's nothing mathematically super special about the number 7. You might say "it's a prime, and also X, Y, Z", but there's pretty much an infinite number of properties you could find for any number you choose.