Please note that very few dancers have 180 degree turnout from their hip joints, resulting in no strain no pain 180 degree turnout in their ballet foot positions.
Yet, there comes a time in your ballet training years where you must stand in a toe-to-heel fifth position. Exactly when that year is, is up to your ballet teacher.
This is the best book for understanding turnout:
You've done years of leg and hip flexibility exercises to improve your turnout. If you're "born to dance", your hip joints, where the top of your thigh fits in, and is attached, slant sideways, as opposed to slanting a little forwards, blocking your movement towards the 180 degree angle, and giving you the ideal ballet foot positions.
Even with those sideways hip joints, you maybe had to do a lot of leg flexibility exercises, to really take advantage of what you were given.
But what if your hip joints aren't quite so sideways pointing, and you feel a pull when you do hip flexibility exercises?
If you're studying Vaganova technique, you probably have been putting your ballet foot positions into the toe-to-heel fifth position since day one.
If not, you may have a ballet teacher who starts with third position, training your leg and hip exercises to improve turnout gradually. Then, crossing over toward fifth position a little at a time.
Decisions need to be made during your training, as to how you will go after your ballet foot positions - or dance turnout in general - and how you fulfill the ideal of "square hips square body".
Every ballet teacher must evaluate every individual ballet student and determine how and when she/he will demand those anatomically incorrect ballet foot positions.
Especially for adults ballet classes, this topic should be addressed.
Get your copy of "Tune Up Your Turnout" and you'll have good ballet foot positions.