1. You are a girl aged between 13 and 19 years old.

Question

(Which one is missing between 'girl' and 'aged'? is #1 from #2?)

2. You are a girl who is aged between 13 and 19 years old.

Answer 1

Both sound really wrong. We'd never say either.

You are a girl between the ages of 13 and 19. (The "years old" is redundant, but can still be put in there.)