Re. the GP's comment though - I don't understand how you could do this without any savings, there must've been some? At least rent (assuming you don't live with parents), food, internet connection - it has to be paid somehow surely - either by "you" (through savings) or family/friends taking the hit (eg letting you crash, using their facilities). With the right setup and network you could live extremely cheaply but someone is going to be paying for it. I don't think this is limited to rich kids or upper middle class teenagers (not sure of the focus on children rather than independent adults?) - if the average person can save for a holiday or whatnot - they could equally save towards living expenses, even if only "paying for my own food whilst I stay on my friends sofa rent free".
I'm personally planning for an exit strategy which will see me working for myself in about 6 months time. I have roughly one year's take-home pay and will ideally have 18-24 months by the time I quit.
There's no need to keep that much money in the bank just in case you lose your job and can't pay your mortgage. Most lenders (at least where I'm from) will arrange a payment holiday if you tell them you've lost your job. After all, they benefit by earning more interest whilst you're not making payments.
Of course, there are many other good reasons to want that much liquid cash in the bank.
I certainly don't drop every dollar into my mortgage every month, it's just not worth the risk for a potential 4% return on investment.
Basically quit your day job only if your side hustle is already making more money per month (not per hour) because odds are even making more per month is still going to result in not being able to survive much past 57.
Side note, how many 57 year old indie game devs are there?
The average American doesn't do what is "conventional wisdom".