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.
If a person does not have any source of income, how will his discretionary fund be created? If someone wants to invest in Bitcoin, then he must first have an income source. After that, he must have discretionary income. Which will survive after all the expenses of his family. He will invest with that extra money. If someone does not have income, then he will not have a discretionary fund and if he does not have it, it will not be right for him to invest. Without discretionary income, if you use your own needed money or borrow money from somewhere and invest in Bitcoin, it will be trading or gambling. If you invest in Bitcoin and continue to invest for a long time without selling Bitcoin, then it is possible to get a lot of profit.