He loves hiking. You don't. You both know if you went you'd hate it.
It's understandable that you'd feel upset that he wants to do something that you don't - and you don't want him to go.
He's staring 70 in the face. If he doesn't do it now, it will probably never happen.
The chance to do something amazing, probably the last opportunity he'll have before time, fitness and health begin to run out, is becoming very pressing.
And if he doesn't, it'll be you who stopped him.
Plus the Camino has a strong spiritual element. Is he exploring something spiritual within himself that he feels a need to do? Something missing?
Stop standing in his way. You don't need to be joined at the hip.
Plan something you want to do - and he wouldn't. A trip with friends, family. Experiences that would suit you.
And plan something for after those separate trips for you to do together. To each hear about what the other did and loved doing.