Generational differences are real. Learning styles and attitudes of people who grew up in the 40s, 60s, 80's, etc., often differ significantly. This should be considered in your training design when you expect the end users to vary widely in age. As an Instructional Designer, you should seek out information in the form of academic studies, books, and articles that provide insight into these differences.

In practicality, it may not be possible to address all of these differences, but sometimes you can accomplish a lot with a little effort. For example, in an eLearning offering, you may be able to provide supplementary information that will be of great assistance to certain persons, and do so in a way that learners who do not need this information can bypass it. As with all practical considerations in training design, the key is to find the right balance.