There is a reason graybeards are valuable. It's not that they're over 50 or 60. It's experience. A full-stack developer with 20 years' worth of experience will not make certain kinds of mistakes.
But hell, the unconventional is increasingly becoming the conventional. Some of the best advice I ever received was from a doctor I had when I was young. He was an old Jamaican man who went from the slums of Kingston to Chemical Engineering in the US to a practicing MD (physician, general practitioner) in a small town in Canada. He just said (kind of what you'd expect from a Jamaican man): not to worry about anything.
Just do things, make messes, clean them up, do more things. You just might do some good in the process.
In the modern dev shops now the soft skills you've developed in the additional years you've had before getting into development will give you quite an advantage since 99% of places aren't just heads down coding anymore.
Where I've found I have a disadvantage is in my non-work commitments and free time outside of work. The younger guys can spend their evenings and weekends working on side projects, going to hackathons or just learning something new, whereas I come home to the family and try to spend quality time with them, do my share of the work in the upkeep of the house, yard, etc.
We only get one shot at life so you're never too old for anything in terms of what you want to spend 40+ hours a week doing to finance your life.
Just be willing to learn from those who are more proficient than you, even if they are younger.
You'll soon catch up.
On top of that, while you might learn slower, you probably attended more classes and played less video games during them than 90% of the twenty year olds.
Back then, there was no separation of front end, back end or database - it was all melded into one, so if I wanted to write an app, I would have to learn the language, figure out how to display the data and collect user input from the screen, write the data tables and the code to update it etc. etc.
There was no question of learning SQL or raw file system I/O to manipulate data - there was no ORM or framework to fall back on. Until Windows came along, there was no standard on UI or UX principles. It was all 'build it as you go'.
Some of those older habits die hard. Though I use ORMs almost all the time now, I still find myself experimenting with queries in raw SQL before translating them to my ORM of choice. I still have a hard time separating my front end code, or the design elements thereof, for someone else to do, because I am so used to doing it myself.
Somehow, I still feel the need for ownership of all aspects of my application stack, and will often spend an inordinate amount of time learning about something that I am not familiar with. As I said before, Old habits die hard.
So, while I don't often refer to myself as a 'full stack developer', I do routinely say that I 'do it all, including making the coffee and sweeping the floor in the server room'.
We catch the things that fall between the cracks; we are the glue that binds together the things that fall apart; we are the toolmakers, the automaters, the pinch-hitter sysadmins; we are problem solvers, the ones that do whatever it takes - and if we don't know how, we learn.
Younger devs have it made in that regard. And the amount of tutorials and quality are amazing these days. They do have a lot more technologies to learn though.
Times change and so does language, true to any old fart out there, and the old farts to be.
I thought it was the other way around. With ML taking a more statistical approach to traditional AI problems.
I actually like the term "full stack developer". I take it to mean: can handle anything from assembly to HLL and everything in between.
I like that - may I use it?
-- 58 year old full-attack dev