It also depends on lifestyle and choices made.
Clearly.
Loans like car, personal and mortgages will seriously eat into any monthly income
In my country the people, after starting to have a steady income, usually at late 20s and in the 30s, take a loan and buy a flat.
Usually one has to pay some 20-30 years for that, hence if one took a loan for his flat in the past 10 years, not much of a chance for bitcoin either

But my point in the other post was not about that. My point was about the country. In some countries the minimum wage is low. In mine the minimum legal wage will rise next year to some 600 EUR.
A 20 years old person is a newbie in his field and will not have a great starting salary.
Taking all this into account, neither the $3k/month logic, nor the "living frugally" to save some bitcoins don't help.
What can help is a second job. But I think that in the 20s that's not an easy step to make.
600 per month minimum wage is very low, $3000 per month is quite substantial.
The monthly minimum wage in my country is approximately 1750.
Taking a second job would be necessary in order to live and save or buy Bitcoin,
it's not an easy step and can be very demanding but if the person is focussed on Bitcoin
the second job may only have to be temporary.