There are young people today that move like old people from eating too much junk food and not getting enough exercise.
Don't worry. These poses have nothing to do with meditation or enlightenment.
Without the Yamas, known as the ethical rules, there is no success in Yoga
Don't teach too many postures; just the main ones, and hold them for a long time.
Always remember that Nature refuses to be rushed. She can only be made to evolve and that takes time, so take heart.
Every time you have a chance, go within and do your meditation.