If you have been in a job for a while and are finding as you get older that you are no longer able to cope with either the physical or mental demands of the role you may want to explore the different options that are open to you. This is quite a common issue, and some companies are accommodating and may be able to move you into a different role within the company however if this is not the case it may be that you need to look for different employment to protect your health and wellbeing.
The first thing to do is to honestly look at the skills you have and whether they are transferable to another role. For instance, if you worked in a customer facing role in a bank and enjoyed this aspect of the role you may be able to use those skills to work in retail or as an outreach worker for a charity. Good organisational skills are valuable in lots of roles and are easily transferred to different jobs.
If you are in receipt of your pension and so do not need to bring in a regular income from employment it is worth looking at the voluntary sector as they are always desperate for skilled people to offer their services. This can be tremendously rewarding and working in a team brings with it the friendship and camaraderie that we often value in our senior years.