Modern Western yoga approaches are not based on any particular belief or religion.
The Yoga Sutra is a compilation of 195 statements that essentially provide an ethical guide to living morally and embracing the science of yoga.
Due to the concise style in which the sutras are written, students must rely on the guru to interpret the philosophy contained therein.
All types of yoga have sequences that you can practice to target different parts of the body
Pranayama Yoga: Respiratory regulation, prolongation, dilation, length, dilation and control explain the mechanism of action of pranayama yoga.
Power Yoga: Power Yoga has been devised through the teachings of Sri K. Pattabhi Jois, a renowned Sanskrit scholar who inspired Western Yogis with his Ashtanga Yoga Style and philosophies.
Bhakti Yoga: Bhakti yoga has many phases to its practice. Bhakti means “devotion,” and Guna Bhakti is to worship according to your nature.
Iyengar Yoga: Iyengar Yoga was developed in India by B.K.S Iyengar, born 14th December, 1918. At 16, he was introduced to yoga by his Guru Sri T. Krishnamacharya.
Purna or Integral Yoga: Integral yoga is a yoga of synthesis, harmonizing the paths of karma, jnana, and bhakti yogas. Swami Satchidananda developed it.
Sivananda Yoga: Sivananda Yoga offers a gentle approach. It includes Meditation, chanting, deep relaxation in each session.
However, from the short explanations of each, you can see that Yoga practice can differ dramatically.
You are never too old to start yoga. I have met people in their seventies, beginning for the first time and experiencing life-changing effects.