Is yoga considered to be good exercise? will it help me stay fit?

Yes and yes!: Yoga can be great form of exercise. You will develop good flexibility (which will prevent injuries), lower your stress level, and also help with back and other joint pain. It doesn't hurt to also incorporate some aerobic activity like jogging, walking, elliptical or swimming. Have fun!

Yes!: Not all "yoga" is created equal! some forms emphasize aerobics and static muscular contraction, others a more gentle, and gradual, series of stretching exercises. Both offer positive health benefits, such as improved flexibility, aerobic conditioning, and above all, enhanced neuromuscular integration.

Yes,yes: The only thing to be careful of is overstretching, and losing the functional strength of the muscles. Not too common. Yoga is excellent, and you can do it for life !