Discussion of Phobias. A phobia is a persistent, irrational fear of a specific object (spiders, snakes, etc) or situation (crowds, open spaces, etc). Accompanying this fear is a strong desire to avoid the object or situation.
I don't like aging either. Most of my friends are either 10 years older or 10 years younger 🤣 So they can't relate to me very well. Yes, 35 is objectively quite young. But, you don't have to BE old to FEEL old. Don't let people dismiss your worries. They are real to you. For example I, at 22, suddenly realized my youth was over (or so I thought) and was so depressed for months. Nobody took me seriously. It was terrible. I hope you find people who are understanding to you 🙂
I agree, unlikely a brain tumor. I've also heard that, what MARC said. The reason being that a brain tumor, when it's large enough to cause pain, is definitely large enough that it's almost certainly causing other more telling symptoms of such a tumor.
Sinuses, allergies and tension are all much more likely - and any combination of those three will exacerbate it. Poor sleep habits / quality can contribute to frequent headaches, as can too much caffeine, alcohol, etc.
I'd recommend daily stretching and other exercises. Take it easy at first if you're not used to it, don't overdo it.