I will clear dis up.
You are legally a child/minor if you are under the age of 18 is most countries.
Teenager is NOT a legal categorization, it is applied to a social term representing a subdivision of minors whom have ages which end with 'teen.' It can also be applied to "that" (being cryptic)
Preteen/Pre-teen is a social term representing a minor who is almost a teenager. This applies to 12 and some 11 year olds.
Tween is a social term representing a minor in beTWEEN teen age and child. This applies to 10, 11, and 12 year olds.
Scientifically, humans are REAL adults at the age of approximately 23 on average.