Very interesting question! It's something I have been wondering too. It's something we all have probably thought about at some point. I read that ancient Egyptians knew about tinnitus 2000 years BCE. So it's been around for over 4500 years!
I would love to see some statistics on tinnitus for the past 100 years at least. But then again, who's keeping track? No one seems to care enough. It's not a "disease" and "you can learn to live with it". The attitude by medical professionals is totally disgusting!
It's only in last few decades that we have seen an increased interest, mainly thanks to researchers, many of whom actually suffer from tinnitus themselves. I would also attributed it to rise in number of tinnitus cases and new communication technologies like the Internet.
In many countries, the local support groups are very small, and that makes them feel like they are alone. Many don't even have a website. It's only when they reach out to other sufferers in other countries that they realize that their number is much larger.
I knew almost nothing about tinnitus until I got it. I knew about "ringing in the ears" but I never knew that this is the same thing as "tinnitus", or that this thing could become permanent.
I would say that tinnitus is on the rise. Definitely! The growth curve is likely exponential.
Is it affecting younger people more than before? Definitely! Many educational videos I have seen talk about people in their 60s. By that measure I am already there, and I am only in my 30s. My audiogram is very much normal by the way, but a few noise recent incidents may have caused me hidden hearing loss at around 6 kHz.
How many people I know with tinnitus? If temporary "ringing of the ears" that comes and goes counts, then that would mean pretty much everyone I know. I would call that tinnitus, even if it's not permanent. That's where you have to start if you want to prevent it. But you need to be educated to recognize it as a pathological sign. I wasn't, I didn't! In fact we used to play a guessing game when the ear rings for one of us, where the other person tries to guess if it's left or right ear. I didn't recognize that as "tinnitus".