What does "in single digits" mean here?

Question

"One day, while I was in single digits, he suggested we play catch in the front yard." What does "in single digits" mean here? Thank you.

Answer 1

No baby inside

Answer 2

might mean a bad mood, need the previous couple of lines

Answer 3

Of an age that requires only one digit, 1 - 9.

Answer 4

Less than 10 years old.