It has been my experience that new riders are not all <30 and many of the <30 new riders are starting out on dirt bikes, scooters, and some of these great little bikes being produced today. I have bought and sold over 40 bikes the last 5 years and have seen the full spectrum of riders. I often dissuade new riders from buying some of my bikes because I don't want them to have a bad first experience and advise them on a good first bike for them individually. In the last year I have sold bikes to numerous new riders and nearly all have been older than me, I am not under 30. Just last week I advised a friend, who is about my same age, on which new bike he should buy as his first.
As far as new bikes needing to be bought for used bikes to be sold, the older, more financially mature enthusiasts noted by Data Dan graphs are still buying new bikes. I just bought a nearly new, less than 300 miles bike, from an owner at least 20 years my senior, who had bought it brand new.
Point being I still don't see what's being expressed in this thread, for the most part, and I am on the "front lines" so to speak. Now that being said we are experiencing a unique event negatively affecting the entire world so we will probably see interest in lot's of things decline overall this year :thumbdown so you may be right, technically, once the 2020 sales and ownership numbers are published.