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.
You having a discretionary income has to do with monthly income, it has to do with self discipline and management on how you spend whatever money that comes to you, if not you still will not be able to have discretionary income that you will use in investing in bitcoin,there are a lot of persons that does not have a monthly income, but seasonal and periodical yet tends to do better in their investment than those monthly income earners because they believe that they don't have a constant flow of income and so they plan their investment budget towards their seasonal or periodic income which they will successfully achieve, But for the monthly earners, they feels they are always on funds therefore keep paying attentions on things they don't really need at the moment and ends up procrastinating or giving excuses of insufficient funds, no matter how little your monthly income is, if you are determined or see bitcoin investment necessary and important to you, you will work towards it and achieve it using the stress free strategy DCA.
Some persons really don't have any type of job be it monthly or seasonal, yet they are able to invest from what ever they get from friends and well wishers, family members before they start having their own personal income like joining any signature campaign in the forum or getting any other job .
What about a student that decided to save our of his little pocket money in other to invest in bitcoin from the beginning of his entry point in school,by his graduation he must have gotten some reasonable amount of bitcoin in his portfolio, it all depends on how you plan your life to be.