This is certainly a cautionary tale. I never knew that such a problem existed. I'll be sure to know what a program will run on before buying!
I am very sorry you are having this problem. I have an generation 1 iPad too and most new apps can't be used on it. Whenever I try to download something new I get the message I need a newer operating system, but anything higher than 5 is incompatible with the old iPad.
So I don't even try and buy something for it.