There is a very strange theory that many (or most) girls have the ability to change their apparent physical ages. Otherwise, they are normal.
They can do this for a relatively short time, by mental control of their body. We don't know how it works. Mostly, they use this power to become older before returning to their real age. At the end, they don't will themselves to shrink back down. It's more like the effect rapidly wears off.
Most who can do this, don't know that they can.
It may happen to many girls while they are dreaming, but they always return to normal by morning. Those things are not talked about. The only evidence is ripped or torn night clothes.
A few discover their ability by accident during their childhood or the tumult of their early teen years...
According to the stories, ageshifters can grow older as you're talking to them. You may notice her head rising, as if her body is being lifted up. Her face doesn't seem to change much at first.
She may subconsciously alter her voice to hide the process. All girls can sound younger than they really are.
The shoes are usually the first to be damaged, first bulging uncomfortably, before the laces are torn out and the soles separate, and the toes break through.
Because of the intense concentration involved, they may not notice their clothes becoming overstretched and buttons popping. Sometimes they are completely indifferent to such things.
Most ageshifters first experiment with their powers alone in their room, or sometimes with others.
Ageshifting may also happen unexpectedly, or be caused by strong emotions. Anger can cause them to become older without noticing at first. They say that when an age shift happens because of strong emotions, the experience is more traumatic.
Almost all ageshifters hide their ability for reasons that aren't understood. It's been said the Criss Angel "Mindfreak" segment was actually real...
People always treat them differently after they see it happen, both their friends and family, and those of the opposite sex. Nothing can ever be the same again.