AAA provides a website dedicated to helping seniors remain licensed drivers: seniordriving.aaa.com. On this site senior learners can find tools and resources that can help them with tasks such as evaluating their ability to drive and finding courses to improve driving skills.
Under AAA's Maintain Mobility & Independence section, they specifically reference online defensive driving courses. Under Tools & Additional Resources users can find a number of online driving improvement courses.
Another online option for study guides for the driver license test is golocal.net. This site provides drivers with free study guides by state including information on standard, motorcycle and commercial licenses.