As I know it started with 20 years but later corporations lobbied to extend that to 70 and more.
I also do not share works that the artist told me not to share, but also I do not pay to those works. However, if I was forced to pay to get something I would definitely share everything as compensation and revenge for coercing me to pay.
You confirm what I say in another paragraph because you claim that you pay to support artists not to gain access to their work And that is great.
But the issue which I present is different, as an artist is coercing you to pay him (almost at the gunpoint) which changes relationship type. So it is no longer cruel or immoral to distribute what you obtained.
Also considering how you spent your money, how much of it you spent on artists who hide their stuff behind paywalls and how much you spent on those who give it for free? if those who work for free got more money they probably also could be able to create more and better quality works. But unfortunately, those who decide to share their work get only a fraction of income than those who use paywalls even if those with paywalls have only handful of people who see their work while those who give it for free have hundreds or thousands of fans.
also, the fact that you only recently started paying does not change economic principles. You still will spend a fixed amount of money which you have available and that money will be somehow distributed between different artists you support.
by the way I am also thinking about how it could be possible to get some money because it would be nice if that could become my main job, but hiding stuff behind paywalls is a bad idea for me.
So I consider partial paywall where anyone who wants to get it for free can get it if they just ask individually, or if they don't want to ask they can pay. This is because most people who pay, seem to be totally unwilling to interact with the artist in any way they do not even leave any comments they just want quick consumption.
So for me, it will be that either you pay for access or you write an email and say that you don't want to pay and want it for free and you will get it.