The web is no longer the exclusive property of the young and neither does it look unusual to see an older person on their smart phone. Furthermore, the baby boomers are today's biggest online spenders and therefore represent a segment of society that cannot be ignored.
The needs of older users can significantly impact upon their user experience and therefore good website design must incorporate the requirements of older adults.
Good website design
There are some principles of good website design that stand true for all users but are particularly pertinent for the older demographic. For example, low contrast between text and the background is a problem for users whose colour and contrast perception has degraded.
Small click targets may be difficult to click due to reduced motor control. Visual, physical as well as auditory impairments are more common as we age and thus impair our ability to interact with websites.
Many websites, in the desire to look modern, use grey text on a light background. Whilst this a problem for older users, poor contrast is a problem for everyone. For example, using a mobile phone or laptop in bright sunlight. Some users however need low contrast. Fortunately, modern browsers allow text, colours, and sizes to be changed but it doesn't mean we can ignore the needs of those outside of the mainstream.
Contrast checker
Web Content Accessibility Guidelines address the needs of those with disabilities. If I as a website designer feels that my client wants a design that will break accessibility guidelines then I will offer guidance. These matters can often be subjective and just how little contrast is too little? Well thankfully the WCAG specifies contrast requirements for good usability.
http://webaim.org/resources/contrastchecker/