I’m 20 and no-code is going pretty well for me - I dabble in custom code for APIs to offload WU intensive tasks off of Bubble but mainly low-code. I know of a few experienced people here that are similar, but most of the active people here are 30+ (well, I’m judging profile pictures so hopefully I’m not too far off…). I only know of one that is about my age.
Why’d I start with Bubble instead of code? I used Bubble because it was easier and quicker to build than code. I’m by no means the most experienced Bubble developer in the world - I explored Bubble just over two years ago, started building properly only one year ago, and started doing it for clients a few months ago. I was able to do that so fast purely because young people can learn much quicker (looking back on some of my old topics is a bit embarrassing, this is a fairly basic question and is only from 11 months ago, and here’s me not knowing how to multiply something by -1 exactly 1 year ago to the day! 
Shoutout to @adamhholmes for dealing with those).
Now, (and I’ve only realised now that you’ve mentioned it), all of the people who have half-finished existing apps that they’re stuck on after developing it themselves and ask for my help do tend to be 40+. I’m not particularly sure why. One theory is that they’re more likely to be trying to build a product (startup founders are older more than younger despite what the media would have you believe) as you identified. Part of this is probably that the young ones also get stuck, but just can’t afford to pay someone to finish off their app.
Another is that young founders often meet in university where they can grab a technical cofounder from the CompSci department. That might mean that these startups/products generally use code. Managers that identify a problem and decide to build their solution don’t have that network into the technical space, so they search ‘how to build own app with no code’ and end up here.
Just my two (probably slightly more than two) cents. I’m actually curious what the age makeup of experienced developers is here and also the age demographics of Bubble as a whole and the reasons for that.