My mother developed severe osteoporosis in old age. I've heard that exercise can help me keep my bones stronger.

Walking is great for your body and your mental health. If you don’t have a pedometer, invest in one. Check out sporting goods stores, stores such as Target, or go online to digiwalker.com or accusplit.com.
Gradually build up to at least 10,000 or 5 miles. Remember, this number includes every step you take so be sure and wear your pedometer. Intervals are also a great way to give your metabolism and calorie burn an extra push. Here’s what you do. After you warm up and walk for a few minutes, increase your intensity to where you push yourself hard for about two minutes. In other words, walk fast so that after two minutes you are ready to slow down again. Then recover to your usual pace. Do this several times during your walk.