You are right. It is all a matter of attitude.
I have always maintained that cruising is for old folk. The space on a boat is restricted and younger people just will not get enough exercise. Even we (the old) have to do something about this.
I was born in 1940 and I am building a sea boat here
. I hope to launch her in a few month's time and then cruise 'open ended' and certainly with no retirement plans.
I am already adjusting my life. I have stopped drinking alcohol, I exercise and I eat healthily. I feel and am better than 5 and 10 years ago. I have also bought a computer and taught myself to make a website. It is a bit behind with updates, but never mind.
I also swim and dive, even in winter. It feels cold for me also, but it can be done.
Old? Many old people are much younger than I!
As you said. It's a matter of attitude.