Aging Workforce

We have an aging workforce and that number is growing.   We have employees who are working well into their 70’s and a couple in their 80’s.  Wondering if anyone out there has any recommendations/policies surrounding this issue.   We do not want to fall into a Human Rights claim based on age discrimination, but we are starting to have some challenges with their productivity.  We are wondering best way to handle as we do not want to necessarily terminate them, but that may come to fruition.  Does anyone out there have any experience with an aging workforce and/or potential policies that protect against age discrimination?