Retirement feels like something you do together as a couple
Well, only if you are the same, or very close in age, or you have planned for this in advance. What is odd here, is the "assuming" that 2 people of a different age, would be retiring at the same time. My starting point would be that people retire at 'retirement age' (State pension age) except where it has been planned otherwise (in terms of having paid off your mortgage, and sorted out generous pensions many years before, or have some asset - like a business to sell that is part of your financial planning.
so you can make plans, travel, take up new hobbies or pursuits.
One thing I always remember my Mum saying is how important she felt it was that she and my Dad both had interests / hobbies / friendship groups in retirement that each of them did independent of each other. She said she had seen too many widows and widowers whose whole world collapsed when their partner died as their whole world revolved around each other and they then struggled to cope with going to anything without their spouse there. I think that is pretty good advice. Yes, I hope we are fit and well enough, and we have made financial plans to be able to afford it, to be able to visit a few places on our bucket list when we retire, but, outside of holidays I am NOT planning to spend 24/7 with dh anymore than we have done for the first 30 years + of our relationship. I don't need to retire at the same time as dh, nor does he need to retire at the same time as me to be able to follow hobbies, volunteering, socialising etc that I plan to do when retired.