If a person has a reasonable source of income and is willing to invest, then he should never delay investing. It is best to start investing first. You can do everything after investing. If you want to learn everything beforehand, then it will be too late to invest, it will never be the right decision. You have to start investing first and then you can learn a lot.
I don't think an investor needs a reasonable source of income to start investing in bitcoin, what an investor needs in other to start investing consistently is a discretionary funds, because their are so many folks out there that are earning quite a lot of money or a reasonable source of income as you claim that still can't invest in bitcoin because they they can't sorts out their discretionary funds, so in my own opinion, what a newbies investor needs in other to start investing in bitcoin is discretionary funds and the basic knowledge on Bitcoin and how to go about your Bitcoin investment.
There is a big difference between reasonable income and discretionary income. The type of income source or the amount of income does not play a significant role in investing. The most important thing is whether the income source can provide you with discretionary money. Even if your income is $10k per month, it will not be suitable for investment if you do not get discretionary money from it. An income source that goes to $1k per month can also be suitable for investment, if it is possible to select discretionary money. That is, the expenditure based on your income will depend on whether your income source is suitable for investment or not. In some places, even though you get high salaries, it becomes difficult to set aside discretionary money due to inflation there. In some places, even though you get low salaries, it is easy to get discretionary money because there is no effect of inflation. This varies from place to place. So, instead of giving importance to the source of income for investment, give importance to the source of discretionary income.