I think you are describing the moment you finally realise that the list of things that are going to give you that magical wow moment, have finally shortened to almost nothing. I would say it is a phase in life not everyone reaches, I still meet people in their 50's to whom a new car, a birthday, a holiday, christmas, valentines day etc etc, all make them magically excited. I often wonder if its just habit for them, and they are too scared to admit it, or if they are honestly that animated by what appears to me to be something that ceased to have any meaning many years ago.
Is having a full life hobbies, a job, children, friends, parties? I think such a life would make me want to die inside very quickly. Like you, I lived a pretty wild life right through to my late 40's, after which everything became meh. For me, now, life is made up of challenges, how do I affect the people closest to me? what can I do to help them? How can I be the best of myself, both physically and mentally, how can I be more understanding, empathetic, patient. Instead of looking for pleasure and happiness each day, I look for work and life challenges, I find myself taking each interaction and experience as a lesson or a test, did I pass, did I fail, did I say the right thing or do the right thing, what actually is the right thing, over and above what current society dictates, what is universally right, what is universally wrong...
I know that I will more than likely never find that excitement and happiness that I had in my 20s/30s, and in a sense it is quite liberating not to be chasing constant happiness, and be content with just living each day as it comes, and learning a bit more about the world, about myself, about the people around me. I am not happy, but I am not unhappy, I am content however.
I don't think its for everyone though...