Good morning! Check out this article in this morning's edition of The Washington Post listing some of the do's and don'ts of exercise.
I know I carp on this a lot, but pay particular attention to the first recommendation: DO LIFT WEIGHTS! It is absolutely critical for bone health, and I am living proof, weight training, testosterone, and Vitamin D optimization cured me of osteopenia (precursor to osteoporosis).
Tip #5 is also important ---- be sure to stretch after exercising! Those of us in our late 40's to 60's were taught to warm up before exercising, and now we know that it's best to stretch after the muscles are warm.