Another thing that will come with age is that making predictions about tech is generally a bad idea. Or at least often doesn't pan out favorably. See Web 3.0 and Crypto.
Regarding what is wise/not wise to learn. Do what feels right and what makes you happy today. You like webdev and the framework-on-framework-on-framework-on-framework-on-dom-on-jit development? Go for it! You like iOS development? Do that.
You can make money either way and earn a comfortable living with experience. The market is wider for "webdev" (too broad of a term encompassing too many technologies) than it is iOS. Your generic run of the mill company may need a webdev, but far fewer are going to need an iOS dev.
If your goal is money and to screw the rest of life and relationships, just look at job postings today and see what the rate is.
Anyway, you're (probably) too young to worry about "what about 10, 20, 30 years from now?" questions. When I was young the Internet didn't seem much more than Compuserve, AOL, and refdesk.com. Could I have predicted that the web would be what it is today? Absolutely not :-)