Advancing in ballet, and into pointe shoes is determined by some finer details other than age, experience and muscle strength. Your ability to concentrate, to form neural pathways (learning new things through concentration and repetition) and to create the correct muscle memory will show that you can go on to pointe work. You must be able to work safely, with no distractions. If you are a little tired, or having an "off day", your ability to concentrate will get you through.
Holding back a young dance student from pointe work, who has the near-perfect physique, allowing for accurate placement and tidy looking exercises, is sometimes advisable.
The extent of muscular strength may not be present yet. Just as important, the maturity and ability to concentrate may not be developed.
The advantage of practising pre-pointe foot exercises is that a student has focused on some finer details of muscle work in the tiny intrinsic foot muscles. These muscles do not get developed well in our footwear, generally.
Specific exercises using the toes like you are playing a piano, or switching off lifting the big toe from the floor, then the other four toes, develop the foot muscles.
But first, the neural pathways are developed. The ability to concentrate on these tiny movements trains the brain to recognize what you want.
Then, after repetitions of the correct movements, the brain connects immediately with the right muscles and the correct movement results. That's muscle memory. And the strength follows.
I've often recommended stretching while you are watching a movie, or studying. Sprawled on the floor with a book, in second position, and slowly stretching and backing off when pain occurs, does not take the same kind of focus.
What you cannot get on the shelf at the ballet store, you can get with practise. Your brain will build neural pathways any way you want. If the technique is accurate, hurrah. If not, you will at some point have to unlearn, and learn again. That is more difficult.
If your power of concentration is not developed, no problem. You just repeat a correctly learned exercise. Your fantastic brain takes over. You feel your muscles and every single part of a movement. THEN you start to build strength.
And when you get into pointe shoes, you already have a better ability to concentrate, a good muscle memory from well built neural pathways, and a measure of control.
Here are some excellent tips and tricks to build strength, muscle memory, when you are dancing in pointe shoes.