Pointe work in ballet is not undertaken lightly. Any ballet student beginning pointe training will typically have had two to three years of prior ballet training, and children aren't placed into pointe training until the age of about 12. Pointe training isn't done any earlier than this because the bones in a child's feet haven't developed fully from cartilage to bone and may not provide enough support, which can cause permanent damage to young feet.
The most important characteristics of the foot when doing pointe work are the structure of the ankle and foot. The ankle must be strong enough to support the weight of the body. The ideal foot for pointe work has toes that are all of close to equal length; this will form a "squared-off" platform that will support the dancer. A foot that has a big toe that is longer than the other toes will experience discomfort and difficulty performing pointe work, as this can result in the big toe supporting the body's entire weight. This, however, is not a hard and fast rule, and this type of foot doesn't necessarily prevent a dancer from doing pointe work.
Another consideration is the amount of flexibility found in the ankle. Also important is the degree of arch in the instep. A dancer who lacks the necessary flexibility and doesn't have enough arch will be unable to perform the key maneuver of placing the ankle in a direct line between the knee and the toes while on pointe. Conversely, if a dancer has highly flexible ankles and very high insteps, this often indicates a weakness in the ankle that may require extra training to strengthen it before attempting pointe work.
The most difficult foot characteristic for pointe work is when the second toe is the foot's longest toe. The more pronounced this difference in length, the greater the difficulty for the dancer to perform pointe work. If the difference is slight, the pointe shoe can be modified to relieve the pressure on the middle toe. If the toe is too long, however, a ballet teacher will likely discourage the student from attempting to learn pointe work at all.