The word nacías is the imperfect form of nacer in the second person singular. There are other translations for this conjugation.
See the full nacer conjugation

nacer

Tenía 16 años cuando tu nacías.
I was 16 years old when you were born.
¿Sabes? Apenas nacías, probablemente no recuerdes la granja.
You know, you were just born so you probably wouldn't remember the farm.
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