Hi Aubrey. There are tons of resources out there. Try Silver Sneakers, AARP and some of the free resources offered by certifying agencies such as ACE, AFAA, NSCA, ISSA, and others. You can also do a basic online search which will turn-up dozens of sources for information (which of course you will need to cull through to determine the efficacy and reliability of what you find). You may also check the Medicare website for their information as well as references to others.
I hope that this helps.
You should be able to find some good articles for older adults written by IDEA here http://www.ideafit.com/fitness-articles/special-populations/older-adults