How do we know Lizbeth is on the verge of becoming an adult?

From the text:

By the time I was fourteen, my brother Joey and I were the only children left at our house, the older ones having left home for early marriage or the lure of
the city, and the two babies having been sent to relatives who might care for them better than we.

And I remember, that year, a strange restlessness of body and of spirit, a feeling that something old and familiar was ending, and something unknown and therefore terrifying was beginning.

I was still child enough to scamper along with the group over rickety fences and
through bushes that tore our already raggedy clothes, back to where Miss Lottie lived.

I did not join the merriment when the kids gathered again under the oak in our bare yard. Suddenly I was ashamed, and I did not like being ashamed. The child in me sulked and said it was all in fun, but the woman in me flinched at the thought of the
malicious attack that I had led.