In the comics, it is quite common for a superpowered character (especially Mutants) to gain their powers or abilities at the onset of becoming a teenager (though usually not below age 14 or 15). This is probably to avoid the inherent dangers of a child or a baby casually using his or her powers in a potentially destructive manner or, if there is one, blowing his or her secret identity. More often, its simply used as a metaphor for puberty.
Having just acquired their powers, very few of these teenagers ever have trouble figuring out how to use them; apparently their powers are just instinctive. This doesn't stop mentor figures from training them to master those abilities, of course.
The concept originated with Marvel Comics' X-Men back in the 1960s.